12 scaling outcomes - oecd...by-country cells through the total item-by-country cells. note that the...

26
12 PISA 2015 TECHNICAL REPORT © OECD 2017 225 Scaling outcomes Results of the IRT scaling and population modeling ............................................ 226 Transforming the plausible values to PISA scales.................................................. 233 Linking error ........................................................................................................... 237 International characteristics of the item pool ....................................................... 237 The statistical data for Israel are supplied by and under the responsibility of the relevant Israeli authorities. The use of such data by the OECD is without prejudice to the status of the Golan Heights, East Jerusalem and Israeli settlements in the West Bank under the terms of international law.

Upload: others

Post on 04-Apr-2020

3 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12

PISA 2015 TECHNICAL REPORT © OECD 2017 225

Scaling outcomes

Results of the IRT scaling and population modeling ............................................ 226

Transforming the plausible values to PISA scales .................................................. 233

Linking error ........................................................................................................... 237

International characteristics of the item pool ....................................................... 237

The statistical data for Israel are supplied by and under the responsibility of the relevant Israeli authorities. The use of such data by the OECD is without prejudice to the status of the Golan Heights, East Jerusalem and Israeli settlements in the West Bank under the terms of international law.

Page 2: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

226 © OECD 2017 PISA 2015 TECHNICAL REPORT

This chapter illustrates the outcomes of applying the item response theory (IRT) scaling and population model for the generation of plausible values to the PISA 2015 main survey assessment data. In the item response theory (IRT) scaling stage, all available items and data from prior PISA cycles (2006, 2009, 2012) were scaled together with the 2015 data via a concurrent calibration using country-by-language-by-cycle groups. However, only results based on the item parameters for the 2015 items are presented here.

RESULTS OF THE IRT SCALING AND POPULATION MODELINGThe linking design for the PISA main survey was aimed at establishing comparability across countries, languages, assessment modes (paper-based and computer-based assessments), and between the 2015 PISA cycle and previous PISA cycles (as far back as 2006, which had been the last time that science was the major domain). By imposing constraints on the item parameters in the item response scaling, the estimated parameters for trend and new items were placed on the same scale, along with items that were used in previous PISA cycles (but not selected for 2015). An additional outcome of the item response theory scaling is that paper-based (PBA) and computer-based (CBA) assessment items can be placed on the same scale. The items generally fit well across countries, allowing for the use of common international item parameters. These international (or common) parameters are what allow for comparability of results across countries and years. However, there are cases where the international item parameters for a given item do not fit well for a particular country or language group, or subset of countries or language groups. In these instances (i.e. when there is item misfit), which imply interactions in certain groups (e.g. item-by-country/language interactions, item-by-mode interactions, item-by-cycle interactions), item constraints were released to allow the estimation of unique item parameters. This was done for a relatively small number of cases across items and groups.

Unique item parameter estimation and national item deletionThe item response theory calibration for the PISA 2015 main survey data was carried out separately for each of the PISA 2015 domains (reading, mathematical, science, financial literacy, and collaborative problem solving). Both science (as the main domain in PISA 2015) and collaborative problem solving (CPS) (as a new domain in PISA 2015) included new items; science also included trend items. All of the other domains included trend items only. Item fit was evaluated using the mean deviation and the root mean squared deviation. Both deviations were calculated for all items in each country-language group for each mode and PISA cycle.

The final item parameters were estimated based on a concurrent calibration using the data from PISA 2015 as well as from previous PISA cycles going back to 2006. There were only a few items in mathematics and collaborative problem solving that had to be excluded from the item response theory analyses (in all country-by-language-by-cycle groups) due to either almost no response variance, scoring or technical issues (either problems with the delivery platform or with the coding on the platform), or very low or even negative item total correlations; Table 12.1 gives an overview of these items.

Table 12.1 Items that were excluded from the IRT analyses

Domain Item Mode Reason

Maths (1 item) CM192Q01 CBA Technical issue

CPS (4 items) CC104104CC104303CC102208CC105405

CBA Very few responses in category 0Technical issue

Very few responses in category 0Low and negative item-total correlation (correlation close to zero)

Note: The problems observed for the items in the table were shown over all countries.

The international/common item parameters and unique national item parameters were estimated for each domain using unidimensional multigroup item response theory models. For analysis purposes, the international/common item parameters are divided into two groups: scalar invariant and metric invariant parameters. Scalar invariant items correspond to items where the slope and threshold parameters are constrained to be the same in both paper-based and computer-based modes. Metric invariant items correspond to items where the slope is constrained to be the same, but the threshold differs across modes. For new items from science and collaborative problem solving, there are no metric invariant item parameters because these were administered only as part of the computer-based assessment; for financial literacy, all items were constrained to be scalar invariant. As such, only scalar invariant percentages are reported in these domains. For each domain, the scalar and metric invariant item parameters represent the stable linked items between the previous and PISA 2015 scales; the unique parameters are included to reduce measurement error. Table 12.2 shows

Page 3: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 227

the percentage of common and unique item parameters by domain computed by dividing the number of unique item-by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/common item parameters was above 90% in cognitive domains with the exception of reading and science. Further, only a small number of items received unique item parameters (either group-specific or the same parameters across a subset of groups) except for reading. In reading, the proportion of scalar/metric invariant international/common item parameters was 89.01%, the proportion of group-specific item parameters was 3.01%, and 7.98% received the same unique item parameters across a subset of countries. For trend items in science, 89.70% received scalar/metric invariant international/common item parameters, while 2.62% received group-specific item parameters, and 7.68% received the same parameters across a subset of countries.

Table 12.2 Percentage of common and unique item parameters in each domain for PISA 2015

Maths Reading Science trend Science new CPS Financial literacy

% of unique item parameters (group-specific) 2.16% 3.01% 2.62% 2.05% 1.85% 4.40%

% of unique item parameters (same parameters across a subset of groups)

3.36% 7.98% 7.68% 4.60% 3.19% 2.69%

% of metric invariant common/international item parameters

33.22% 30.33% 20.96% N/A N/A N/A

% of scalar invariant common/international item parameters

61.25% 58.68% 68.74% 93.35% 94.96% 92.91%

Mode and number of items in the PISA 2015 main survey

PBA: 83 items, CBA: 81 items

PBA: 103 items, CBA: 103 items

PBA: 85 items, CBA: 85 items CBA: 99 items CBA: 117 items CBA: 43 items

Note: Interactions go across modes and cycles; Kazakhstan is not included due to adjudication issues.

An overview of the proportions of international/common (invariant) item parameters and group-specific item parameters in each domain for each relevant assessment cycle is given in Figures 12.1 to 12.6. The figures also provide an overview of the proportion of scalar invariant item parameters (items sharing common difficulty and slope parameters across modes) and partially or metric invariant item parameters (items sharing common slope parameters across modes) with regard to the mode effect modeling described in Chapter 9: dark blue indicates scalar invariant item parameters, light grey (the lighter grey above the horizontal line) indicates metric invariant item parameters, medium blue indicates scalar invariant item parameters for a subset of groups (unique parameters different from the common parameter, but for several groups sharing the same unique parameter), and dark grey indicates group-specific item parameters. In addition, Annex H provides information about which trend items are scalar invariant and which are partially or metric invariant for each cognitive domain. Recall that both scalar and metric invariant item parameters (dark blue and light grey) contribute to improve the comparability across groups, while unique item parameters (medium blue and dark grey) contribute to the reduction of measurement error. Across every cycle and every domain, it is clear that international/common (invariant) item parameters dominate and only a small proportion of the item parameters are group-specific (i.e. dark grey). Results show that the overall item fit in each domain for each group is very good, resulting in a small numbers of unique item parameters and high comparability of the data. There was no consistent pattern of deviations for any one particular country-by-language group. The results also illustrate that the trend items show good fit, ensuring the quality of the trend measure across different assessment cycles (2015 data versus 2006-2012), different assessment modes (PBA versus CBA), and even across different countries and languages. An overview of the number of deviations per item across all country-by-language-by-cycle groups for items in each domain is given in Annex G.

After the IRT scaling was finalised, item parameter estimates were delivered to each country, including an indication of which items received international/common item parameters and which received unique item parameters. Table 12.3 gives an example of the information provided to countries: the first column shows the domain; the second column shows the flag that indicates whether an item received a unique parameter or was excluded from the IRT scaling; and the remaining columns show the final item parameter estimates (for each item, the slope, difficulty and threshold parameters for polytomous items were listed). A slope parameter of 1 indicates that a Rasch model was fitted for these items; slope estimates different from 1 indicate that the two-parameter logistic model (2PLM) was fitted.

Page 4: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

228 © OECD 2017 PISA 2015 TECHNICAL REPORT

Math 2006

Freq

uenc

y50

3010

1030

5070

90

Total item-by-group pairs = 2531 Scalar invariant subset pairs = 109 (4.31%)Country-specific pairs = 16 (0.63%)

Scalar invariant pairs = 2406 (95.06%)

Math 2009

Freq

uenc

y50

3010

1030

5070

90

Total item-by-group pairs = 3059 Scalar invariant subset pairs = 129 (4.22%)Country-specific pairs = 16 (0.52%)

Scalar invariant pairs = 2914 (95.26%)

Math 2012

Freq

uenc

y50

3010

1030

5070

90

Total item-by-group pairs = 5998 Scalar invariant subset pairs = 292 (4.87%)Country-specific pairs = 57 (0.95%)

Scalar invariant pairs = 5649 (94.18%)

Math 2015

Freq

uenc

y50

3010

1030

5070

90 Scalar invariant Metric invariantScalar invariant Subset Country-specific

Total item-by-group pairs = 7022 Scalar invariant subset pairs = 236 (3.36%)Country-specific pairs = 152 (2.16%)

Scalar/metric invariant pairs = 6634 (94.47%)

Reading 2006

Freq

uenc

y60

4020

020

4060

8010

012

0

Total item-by-group pairs = 2113 Scalar invariant subset pairs = 229 (10.84%)Country-specific pairs = 24 (1.14%)

Scalar invariant pairs = 1860 (88.03%)

Reading 2009

Freq

uenc

y60

4020

020

4060

8010

012

0

Total item-by-group pairs = 8153 Scalar invariant subset pairs = 696 (8.54%)Country-specific pairs = 106 (1.3%)

Scalar invariant pairs = 7351 (90.16%)

Reading 2012

Freq

uenc

y60

4020

020

4060

8010

012

0

Total item-by-group pairs = 3801 Scalar invariant subset pairs = 290 (7.63%)Country-specific pairs = 19 (0.5%)

Scalar invariant pairs = 3492 (91.87%)

Reading 2015

Freq

uenc

y60

4020

020

4060

8010

012

0

Total item-by-group pairs = 8912 Scalar invariant subset pairs = 711 (7.98%)Country-specific pairs = 268 (3.01%)

Scalar/metric invariant pairs = 7933 (89.01%)

Scalar invariant Metric invariantScalar invariant subset Country-specific

• Figure 12.1 •Frequencies of international (invariant) and unique item parameters in maths

(note that frequencies were counted using item-by-group pairs)

• Figure 12.2 •Frequencies of international (invariant) and unique item parameters in reading

(note that frequencies were counted using item-by-group pairs)

Page 5: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 229

Science 2006

Freq

uenc

y70

5030

1010

3050

7090

110

Total item-by-group pairs = 6148 Scalar invariant subset pairs = 585 (9.52%)Country-specific pairs = 60 (0.98%)

Scalar invariant pairs = 5503 (89.51%)

Science 2009

Freq

uenc

y70

5030

1010

3050

7090

110

Total item-by-group pairs = 5079 Scalar invariant subset pairs = 473 (9.31%)Country-specific pairs = 25 (0.49%)

Scalar invariant pairs = 4581 (90.19%)

Science 2012

Freq

uenc

y70

5030

1010

3050

7090

110

Total item-by-group pairs = 4602 Scalar invariant subset pairs = 438 (9.52%)Country-specific pairs = 34 (0.74%)

Scalar invariant pairs = 4130 (89.74%)

Science 2015

Freq

uenc

y70

5030

1010

3050

7090

110

Total item-by-group pairs = 8650 Scalar invariant subset pairs = 664 (7.68%)Country-specific pairs = 227 (2.62%)

Scalar/metric invariant pairs = 7759 (89.7%)

Scalar invariant Metric invariantScalar invariant subset Country-specific

New Science 2015

Freq

uenc

y

5030

1010

3050

7090

110

Scalar invariant Scalar invariant subset Country-specific

Total item-by-group pairs = 8213

Scalar/metric invariant pairs = 7667 (93.35%)

Scalar invariant subset pairs = 378 (4.6%)

Country-specific pairs = 168 (2.05%)

• Figure 12.3 •Frequencies of international (invariant) and unique item in trend science

(note that frequencies were counted using item-by-group pairs)

• Figure 12.4 •Frequencies of international (invariant) and unique item in new science

(note that frequencies were counted using item-by-group pairs)

Page 6: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

230 © OECD 2017 PISA 2015 TECHNICAL REPORT

Collaborative problem solving 2015

Freq

uenc

y

4020

020

4060

8010

012

014

0

Total item-by-group pairs = 8742

Scalar/metric invariant pairs = 8301 (94.96%)

Scalar invariant subset pairs = 279 (3.19%)

Country-specific pairs = 162 (1.85%)

Scalar invariant Scalar invariant subset Country-specific

Financial literacy 2015

Freq

uenc

y

200

2040

60

Total item-by-group pairs = 818

Scalar/metric invariant pairs = 760 (92.91%)

Scalar invariant subset pairs = 22 (2.69%)

Country-specific pairs = 36 (4.4%)

Scalar invariant Scalar invariant subset Country-specific

• Figure 12.5 •Frequencies of international (invariant) and unique item in CPS (note that frequencies were counted using item-by-group pairs)

• Figure 12.6 •Frequencies of international (invariant) and unique item in financial literacy

(note that frequencies were counted using item-by-group pairs)

Page 7: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 231

Table 12.3 Example of table for item parameter estimates provided to the countries

Domain Flag Item Slope Difficulty IRT_Step1 IRT_Step2

Maths PM00GQ01 1 1.62226

Maths PM00KQ02 1 1.11572

Maths PM033Q01S 1 -0.95604

Maths PM034Q01S 1 0.15781

Maths Unique item parameters PM155Q01 1.42972 -0.35538

Maths PM155Q02 1 -0.35727 -0.42436 0.42436

Maths PM155Q03 1.08678 0.73497 -0.20119 0.20119

Maths PM155Q04S 1 -0.27556

Maths PM192Q01S 1 0.20948

Maths Excluded from scaling PM936Q01

Generating student scale scores and reliability of the PISA scalesGiven the rotated and incomplete assessment design, it is not possible to calculate marginal reliabilities for each cognitive domain. In order to get an indication of test reliability, the explained variance (i.e. variance explained by the model) for each cognitive domain was computed based on the weighted posterior variance. The variance is computed using all 10 plausible values as follows: 1 – (expected error variance/total variance). The weighted posterior variance is an expression of the posterior measurement error and is obtained through the population modeling. The expected error variance is the weighted average of the posteriori variance. This term was estimated using the weighted average of the variance of the plausible values (the posteriori variance is the variance across the 10 plausible values). The total variance was estimated using a resampling approach (Efron, 1982). It was estimated for each country depending on the country-specific proficiency distributions for each cognitive domain.

Applying the conditioning approach described in Chapter 9 and anchoring all of the item parameters at the values obtained from the final IRT scaling, plausible values were generated for all sampled students. Table 12.4 gives the median of national reliabilities for the generated scale scores based on all 10 plausible values. National reliabilities of the main cognitive domains based on all 10 plausible values are presented in Table 12.5.

Table 12.4 Reliabilities of the PISA cognitive domains and Science subscales overall countries1

Mode Domains Median S.D. Max Min

CBA

Maths 0.85 0.03 0.90 0.75

Reading 0.87 0.02 0.90 0.80

Science 0.91 0.02 0.93 0.82

CPS 0.78 0.03 0.83 0.70

Financial literacy 0.83 0.06 0.93 0.72

Science subscales

Explain phenomena scientifically 0.89 0.03 0.91 0.80

Evaluate and design scientific inquiry 0.87 0.04 0.90 0.71

Interpret data and evidence scientifically 0.89 0.03 0.92 0.78

Content 0.89 0.02 0.91 0.81

Procedural & epistemic 0.90 0.03 0.92 0.78

Earth & science 0.88 0.03 0.90 0.77

Living 0.89 0.03 0.91 0.79

Physical 0.88 0.03 0.91 0.76

PBA

Maths 0.80 0.05 0.87 0.67

Reading 0.82 0.04 0.88 0.72

Science 0.86 0.04 0.92 0.77

1. Please note that Argentina, Malaysia, and Kazakhstan were not included in this analysis due to adjudication issues (inadequate coverage of either population or construct).

Page 8: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

232 © OECD 2017 PISA 2015 TECHNICAL REPORT

Table 12.5[Part 1/2]National reliabilities for main cognitive domains

Mode Country/economy Maths Reading Science CPS Financial literacy

CBA Australia 0.84 0.86 0.92 0.76 0.93

CBA Austria 0.87 0.88 0.93 0.80 –

CBA Belgium 0.89 0.89 0.93 0.80 0.87

CBA Brazil 0.78 0.82 0.87 0.71 0.72

CBA Bulgaria 0.85 0.88 0.92 0.82 –

CBA Canada 0.83 0.83 0.91 0.74 0.76

CBA Chile 0.86 0.86 0.91 0.78 0.83

CBA B-S-J-G (China)1 0.90 0.90 0.93 0.83 0.88

CBA Colombia 0.82 0.87 0.89 0.76 –

CBA Costa Rica 0.78 0.83 0.85 0.70 –

CBA Croatia 0.86 0.87 0.91 0.76 –

CBA Cyprus2 0.84 0.84 0.90 0.74 –

CBA Czech Republic 0.88 0.88 0.92 0.77 –

CBA Denmark 0.85 0.86 0.91 0.78 –

CBA Dominican Republic 0.81 0.86 0.84 – –

CBA Estonia 0.85 0.86 0.91 0.79 –

CBA Finland 0.85 0.87 0.91 0.77 –

CBA France 0.88 0.89 0.93 0.77 –

CBA Germany 0.86 0.86 0.92 0.76 –

CBA Greece 0.86 0.87 0.91 0.79 –

CBA Hong Kong (China) 0.84 0.85 0.90 0.77 –

CBA Hungary 0.88 0.89 0.92 0.81 –

CBA Iceland 0.83 0.86 0.91 0.76 –

CBA Ireland 0.85 0.87 0.91 – –

CBA Israel 0.87 0.88 0.92 0.83 –

CBA Italy 0.87 0.87 0.91 0.80 0.81

CBA Japan 0.85 0.85 0.91 0.75 –

CBA Korea 0.85 0.85 0.91 0.78 –

CBA Latvia 0.85 0.86 0.90 0.75 –

CBA Lithuania 0.85 0.87 0.91 0.80 0.83

CBA Luxembourg 0.87 0.89 0.93 0.77 –

CBA Macao (China) 0.82 0.86 0.90 0.78 –

CBA Malaysia 0.86 0.87 0.90 0.79 –

CBA Mexico 0.79 0.84 0.86 0.75 –

CBA Montenegro 0.80 0.84 0.88 0.74 –

CBA Netherlands 0.89 0.89 0.93 0.79 0.88

CBA New Zealand 0.85 0.86 0.92 0.79 –

CBA Norway 0.84 0.85 0.91 0.75 –

CBA Peru 0.82 0.88 0.87 0.78 0.87

CBA Poland 0.86 0.87 0.92 – 0.83

CBA Portugal 0.87 0.86 0.92 0.78 –

CBA Qatar 0.85 0.89 0.91 – –

CBA Russia 0.78 0.80 0.88 0.75 0.73

CBA Singapore 0.87 0.88 0.93 0.79 –

CBA Slovak Republic 0.86 0.89 0.92 0.77 0.76

CBA Slovenia 0.88 0.89 0.93 0.79 –

CBA Spain 0.86 0.86 0.91 0.75 0.81

CBA Sweden 0.85 0.86 0.92 0.78 –

CBA Switzerland 0.86 0.88 0.92 – –

CBA Chinese Taipei 0.87 0.88 0.93 0.78 –

CBA Thailand 0.81 0.86 0.88 0.83 –

CBA Tunisia 0.75 0.80 0.82 0.70 –

CBA Turkey 0.82 0.85 0.89 0.74 –

CBA United Arab Emirates 0.83 0.87 0.91 0.80 –

CBA United Kingdom 0.87 0.88 0.92 0.83 –

CBA United States 0.87 0.88 0.92 0.81 0.87

CBA Uruguay 0.85 0.87 0.90 0.78 –

Page 9: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 233

Table 12.5[Part 2/2]National reliabilities for main cognitive domains

Mode Country/economy Maths Reading Science CPS Financial literacy

PBA Albania 0.75 0.79 0.84 – –

PBA Algeria 0.67 0.72 0.77 – –

PBA Argentina 0.79 0.82 0.85 – –

PBA FYROM 0.79 0.79 0.84 – –

PBA Georgia 0.83 0.83 0.86 – –

PBA Indonesia 0.78 0.77 0.82 – –

PBA Jordan 0.78 0.82 0.86 – –

PBA Kazakhstan 0.73 0.71 0.78 – –

PBA Kosovo 0.80 0.81 0.82 – –

PBA Lebanon 0.82 0.85 0.86 – –

PBA Malta 0.87 0.88 0.92 – –

PBA Moldova 0.78 0.83 0.86 – –

PBA Romania 0.80 0.82 0.86 – –

PBA Trinidad and Tobago 0.86 0.84 0.88 – –

PBA Viet Nam 0.83 0.84 0.87 – –

1. B-S-J-G (China) data represent the regions of Beijing, Shanghai, Jiangsu, and Guangdong.2. Note by Turkey: The information in this document with reference to “Cyprus” relates to the southern part of the Island. There is no single authority representing both Turkish and Greek Cypriot people on the Island. Turkey recognizes the Turkish Republic of Northern Cyprus (TRNC). Until a lasting and equitable solution is found within the context of the United Nations, Turkey shall preserve its position concerning the “Cyprus issue.”Note by all the European Union Member States of the OECD and the European Union: The Republic of Cyprus is recognised by all members of the United Nations with the exception of Turkey. The information in this document relates to the area under the effective control of the Government of the Republic of Cyprus.

The table above shows that the explained variance by the combined IRT and latent regression model (population or conditioning model) is at a comparable level across countries. While the population model reaches levels of above 0.80 for reading, mathematics and science, it is important to keep in mind that this is not to be confused with a classical reliability coefficient, as it is based on more than the item responses. Comparisons among individual students are not appropriate because the apparent accuracy of the measures is obtained by statistically adjusting the estimates based on background data. This approach does provide improved behavior of subgroup estimates, even if the plausible values obtained using this methodology are not suitable for comparisons of individuals (e.g. Mislevy & Sheehan, 1987; von Davier et al., 2006).

TRANSFORMING THE PLAUSIBLE VALUES TO PISA SCALESThe plausible values were transformed using a linear transformation to form a scale that is linked to the historic PISA scale. This scale can be used to compare the overall performance of countries or subgroups within a country.

For science, reading and mathematics, country results from the 2006, 2009 and 2012 PISA cycles for OECD countries were used to compute the transformation coefficients for each content domain separately. The country means and variances used to compute the transformation coefficients included only those values from the cycle in which a given content domain was the major domain. Hence, the transformation coefficients for science are based on the 2006 reported and model-based results, reading coefficients are based on the 2009 results, and mathematics coefficients are based on the 2012 results. Only the results for countries designated as OECD countries in the respective PISA reporting cycle were used to compute the transformation coefficients. If mYij is the reported mean for country i in cycle j, mXij is the model-based mean obtained from the concurrent calibration using the software mdltm, and s2

Yij and s2Xij are the reported

and model-based score variances respectively. The same transformation was used for all plausible values (within a given domain). The transformation coefficients for a given content domain were computed as:

12.1

A =τYjτXj

12.2

B = mYj – AmXj

Page 10: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

234 © OECD 2017 PISA 2015 TECHNICAL REPORT

12.3

τYj = τYj2 =

1nj – 1

mYij – mYj2

nj

i = 1

+1nj

SYij2

nj

i = 1

12.4

τXj = τXj2 =

1nj – 1

mXij – mXj2

nj

i = 1

+1nj

SXij2

nj

i = 1

2006 Sciencewhere = { 2009 Reading 2012 Maths

The values and mYj and mXj are grand means of the reported and model-based country means in cycle j, respectively. The terms τ2

Yj and τ2Xj correspond to the total variance, defined as the variance of the country means, plus the mean of

the country variances respectively. The square root of these terms is taken to compute the standard deviations τYj and τXj. The 2015 plausible values (PVs) for examinee k in country i were transformed to the PISA scale via the following transformation:

12.5

PVTik = A × PVUik + B

The subscripts T and U correspond to the transformed and untransformed values respectively.

For financial literacy, country results from the 2012 PISA cycle were used to compute the transformation coefficients. The method used to compute the coefficients is the same as that used for reading, mathematics and science. The key distinction is that in reading, mathematics and science, only results for OECD countries were used to compute the coefficients, whereas, for financial literacy, all available country data were used to compute the coefficients. This decision was made because there were too few OECD countries to provide a defensible transformation of the results. The plausible values for financial literacy were transformed using the same linear transformation as for reading, mathematics and science.

A new scale for CPS was established in PISA 2015. Consistent with the introduction of content domains in previous PISA cycles, transformation coefficients for CPS were computed such that the plausible values for OECD countries have a mean of 500 and a standard deviation of 100. The 10 sets of plausible values were stacked together and the weighted mean and variance (and by extension SD) were computed. Stated differently, the full set of transformed plausible values for CPS have a weighted mean of 500 and a weighted SD of 100 (based on senate weights).

If Xkv is the vth PV {v in 1, 2, ..., 10} for examinee k, the transformation coefficients for CPS are computed as

12.6

A =100τPV

12.7

B = 500 – A Xkv = 500 – AXkv Wkv

nk =1

10v=1

10 Wkvnk =1

12.8

τPV = τPV2 =

Wkv Xkv – Xkv2n

k =110v=1

10n – 1 Wkvnk =1 /n

Page 11: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 235

The grand mean of the PVs, Xkv, was computed by compiling all 10 sets of PVs into a single vector (the corresponding senate weights were compiled in a separate vector) then finding the weighted mean of these values. The weighted variance, τ2

PV, was computed using the vector of PVs as well. The square root is taken to compute the standard deviation, τPV.The plausible values for CPS were transformed using the same approach as that for science, reading, mathematics and financial literacy. The transformations for reading, mathematics, science and financial literacy used the model-based results from the concurrent calibration (IRT scaling) in order to align the results with previously established scales. The transformation for CPS is based on the PVs because this is the first time the results for this domain have been scaled.

The transformation coefficients for all content domains are presented in Table 12.6. The A coefficient adjusts the variability (standard deviation) of the resulting scale while the B coefficient adjusts the scale location (mean).

Table 12.6 PISA 2015 transformation coefficients

Domain A B

Science 168.3189 494.5360

Reading 131.5806 437.9583

Mathematics 135.9030 514.1848

Financial literacy 140.0807 490.7259

Collaborative problem solving 196.7695 462.8102

Table 12.7 shows the average transformed plausible values for each cognitive domain by country as well as the resampling-based standard errors.

Table 12.7

[Part 1/2]Average plausible values (PVs) and resampling-based standard errors (SE) by country/economy for the PISA domains of science, reading, mathematics, financial literacy, and collaborative problem solving (CPS)

Country/economy

Maths Reading Science CPS Financial literacy

Average PV SE

Average PV SE

Average PV SE

Average PV SE

Average PV SE

International average 462 0.32 461 0.34 466 0.31 486 0.36 481 0.95

Albania 413 3.45 405 4.13 427 3.28

Algeria 360 2.95 350 3.00 376 2.64

Argentina 409 3.05 425 3.22 432 2.87

Australia 494 1.61 503 1.69 510 1.54 531 1.91 504 1.91

Austria 497 2.86 485 2.84 495 2.44 509 2.56

Belgium 507 2.35 499 2.42 502 2.29 501 2.39 541 2.95

Brazil 377 2.86 407 2.75 401 2.30 412 2.30 393 3.84

B-S-J-G (China) 531 4.89 494 5.13 518 4.64 496 3.97 566 6.04

Bulgaria 441 3.95 432 5.00 446 4.35 444 3.85

Canada 516 2.31 527 2.30 528 2.08 535 2.27 533 4.62

Chile 423 2.54 459 2.58 447 2.38 457 2.69 432 3.74

Colombia 390 2.29 425 2.94 416 2.36 429 2.30

Costa Rica 400 2.47 427 2.63 420 2.07 441 2.42

Croatia 464 2.77 487 2.68 475 2.45 473 2.52

Cyprus1 437 1.72 443 1.66 433 1.38 444 1.71

Czech Republic 492 2.40 487 2.60 493 2.27 499 2.20

Denmark 511 2.17 500 2.54 502 2.38 520 2.53

Dominican Republic 328 2.69 358 3.05 332 2.58

Estonia 520 2.04 519 2.22 534 2.09 535 2.47

Finland 511 2.31 526 2.55 531 2.39 534 2.55

France 493 2.10 499 2.51 495 2.06 494 2.42

FYROM 371 1.28 352 1.41 384 1.25

Georgia 404 2.78 401 2.96 411 2.42

Germany 506 2.89 509 3.02 509 2.70 525 2.85

Greece 454 3.75 467 4.34 455 3.92 459 3.60

Hong Kong (China) 548 2.98 527 2.69 523 2.55 541 2.95

Hungary 477 2.53 470 2.66 477 2.42 472 2.35

Iceland 488 1.99 482 1.98 473 1.68 499 2.26

Page 12: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

236 © OECD 2017 PISA 2015 TECHNICAL REPORT

Table 12.7

[Part 2/2]Average plausible values (PVs) and resampling-based standard errors (SE) by country/economy for the PISA domains of science, reading, mathematics, financial literacy, and collaborative problem solving (CPS)

Country/economy

Maths Reading Science CPS Financial literacy

Average PV SE

Average PV SE

Average PV SE

Average PV SE

Average PV SE

Indonesia 386 3.08 397 2.87 403 2.57

Ireland 504 2.05 521 2.47 503 2.39

Israel 470 3.63 479 3.78 467 3.44 469 3.62

Italy 490 2.85 485 2.68 481 2.52 478 2.53 483 2.80

Japan 532 3.00 516 3.20 538 2.97 552 2.68

Jordan 380 2.65 408 2.93 409 2.67

Kazakhstan 460 4.28 427 3.42 456 3.67

Korea 524 3.71 517 3.50 516 3.13 538 2.53

Kosovo 362 1.63 347 1.57 378 1.70

Latvia 482 1.87 488 1.80 490 1.56 485 2.26

Lebanon 396 3.69 347 4.41 386 3.40

Lithuania 478 2.33 472 2.74 475 2.65 467 2.46 449 3.15

Luxembourg 486 1.27 481 1.44 483 1.12 491 1.50

Macao (China) 544 1.11 509 1.25 529 1.06 534 1.24

Malaysia 446 3.25 431 3.48 443 3.00 440 3.29

Malta 479 1.72 447 1.78 465 1.64

Mexico 408 2.24 423 2.58 416 2.13 433 2.46

Moldova 420 2.47 416 2.52 428 1.97

Montenegro 418 1.46 427 1.58 411 1.03 416 1.27

Netherlands 512 2.21 503 2.41 509 2.26 518 2.39 509 3.32

New Zealand 495 2.27 509 2.40 513 2.38 533 2.45

Norway 502 2.23 513 2.51 498 2.26 502 2.52

Peru 387 2.71 398 2.89 397 2.36 418 2.50 403 3.40

Poland 504 2.39 506 2.48 501 2.51 485 2.97

Portugal 492 2.49 498 2.69 501 2.43 498 2.64

Qatar 402 1.27 402 1.02 418 1.00

Romania 444 3.79 434 4.07 435 3.23

Russia 494 3.11 495 3.08 487 2.91 473 3.42 512 3.33

Singapore 564 1.47 535 1.63 556 1.20 561 1.21

Slovak Republic 475 2.66 453 2.83 461 2.59 463 2.38 445 4.53

Slovenia 510 1.26 505 1.47 513 1.32 502 1.75

Spain 486 2.15 496 2.36 493 2.07 496 2.15 469 3.19

Sweden 494 3.17 500 3.48 493 3.60 510 3.44

Switzerland 521 2.92 492 3.03 506 2.90

Chinese Taipei 542 3.03 497 2.50 532 2.69 527 2.47

Thailand 415 3.03 409 3.35 421 2.83 436 3.50

Trinidad and Tobago 417 1.41 427 1.49 425 1.41

Tunisia 367 2.95 361 3.06 386 2.10 382 1.94

Turkey 420 4.13 428 3.96 425 3.93 422 3.45

United Arab Emirates 427 2.41 434 2.87 437 2.42 435 2.43

United Kingdom 492 2.50 498 2.77 509 2.56 519 2.68

United States 470 3.17 497 3.41 496 3.18 520 3.64 487 3.80

Uruguay 418 2.50 437 2.55 435 2.20 443 2.29

Viet Nam 495 4.46 487 3.73 525 3.91

See note 2 under Table 12.5.

Page 13: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 237

LINKING ERRORAn evaluation of the magnitude of linking error can be accomplished by considering differences between reported country results from previous PISA cycles and the transformed results from the rescaling. In the application to linking error estimation for the 2015 PISA trend comparisons the robust measure of standard deviation was used, the Sn statistic (Rousseeuw & Croux, 1993); see Chapter 9 for more information on the linking error approach taken in PISA 2015. The robust estimates of linking error between cycles, by domain are presented in Table 12.8.

The Sn statistic is available in SAS as well as the R package robustbase. See also https://cran.r-project.org/web/packages/robustbase/robustbase.pdf. The Sn statistic was proposed by Rousseeuw and Croux (1993) as a more efficient alternative to the scaled median absolute deviation from the median (1.4826*MAD) that is commonly used as a robust estimator of standard deviation.

Table 12.8Robust link error (based on absolute pairwise differences statistic Sn) for comparisons of performance between PISA 2015 and previous assessments

Comparison Maths Reading Science Financial literacy

PISA 2000 to 2015 6.8044

PISA 2003 to 2015 5.6080 5.3907

PISA 2006 to 2015 3.5111 6.6064 4.4821

PISA 2009 to 2015 3.7853 3.4301 4.5016

PISA 2012 to 2015 3.5462 5.2535 3.9228 5.3309

Note: Comparisons between PISA 2015 scores and previous assessments can only be made to when the subject first became a major domain. As a result, comparisons in mathematics performance between PISA 2015 and PISA 2000 are not possible, nor are comparisons in science performance between PISA 2015 and PISA 2000 or PISA 2003.

INTERNATIONAL CHARACTERISTICS OF THE ITEM POOLThis section provides an overview of the test targeting, the domain inter-correlations and the correlations among the science subscales.

Test targetingIn addition to identifying the relative discrimination and difficulty of items, IRT can be used to summarise the results for various subpopulations of students. A specific value – the response probability (RP) – can be assigned to each item on a scale according to its discrimination and difficulty, similar to students who receive a specific score along a scale according to their performance on the assessment items (OECD, 2002). Chapter 15 describes how items can be placed along a scale based on RP values and how these values can be used to describe different proficiency levels.

After the estimation of item parameters in the item calibration stage, RP values were calculated for each item, and then items were classified into proficiency levels within the cognitive domain. Likewise, after generation of the plausible values, respondents can be classified into proficiency levels for each cognitive domain. The purpose of classifying items and respondents into levels is to provide more descriptive information about group proficiencies. The different item levels provide information about the underlying characteristics of an item as it relates to the domain (such as item difficulty); the higher the difficulty, the higher the level. In PISA, an RP62 value is used for the classification of items into levels. Respondents with a proficiency located below this point have a lower probability than the chosen RP62 value, and respondents with a proficiency above this point have a higher probability (that is > 0.62) of solving an item. The RP62 values for all items are presented in Annex A together with the final item parameters obtained from the IRT scaling. The respondent classification into different levels is done by PISA scale scores transformed from the plausible values. Each level is defined by certain score boundaries for each cognitive domain. Tables 12.9 to 12.13 show the score boundaries overall countries used for each cognitive domain along with the percentage of items and respondents classified at each level of proficiency. The decision for the score boundaries for science is explained in Chapter 15; for reading and mathematics the same levels were used that were defined in previous PISA cycles.

Page 14: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

238 © OECD 2017 PISA 2015 TECHNICAL REPORT

Table 12.9 Item and respondent classification for each score boundary in mathematics

Level Score points on the PISA scale Number of items Percentage of items Percentage of respondents

6 Higher than 669.30 27 13.30 1.91

5 Higher than 606.99 and less than or equal to 669.30 23 11.33 6.37

4 Higher than 544.68 and less than or equal to 606.99 50 24.63 13.93

3 Higher than 482.38 and less than or equal to 544.68 41 20.20 20.16

2 Higher than 420.07 and less than or equal to 482.38 39 19.21 21.81

1 Higher than 357.77 and less than or equal to 420.07 12 5.91 18.78

Below 1 Less than 357.77 11 5.42 17.05

Table 12.10 Item and respondent classification for each score boundary in reading

Level Score points on the PISA scale Number of items Percentage of items Percentage of respondents

6 Higher than 698.32 18 7.63 0.70

5 Higher than 625.61 and less than or equal to 698.32 28 11.86 4.96

4 Higher than 552.89 and less than or equal to 625.61 50 21.19 15.45

3 Higher than 480.18 and less than or equal to 552.89 62 26.27 24.14

2 Higher than 407.47 and less than or equal to 480.18 58 24.58 24.36

1a Higher than 334.75 and less than or equal to 407.47 15 6.36 17.92

1b 262.04 to less than or equal to 334.75 5 2.12 9.12

Below 1b Less than 262.04 0 0.00 3.34

Table 12.11 Item and respondent classification for each score boundary in science

Level Score points on the PISA scale Number of items Percentage of items Percentage of respondents

6 Higher than 707.93 13 4.45 0.76

5 Higher than 633.33 and less than or equal to 707.93 29 9.93 4.79

4 Higher than 558.73 and less than or equal to 633.33 75 25.68 14.51

3 Higher than 484.14 and less than or equal to 558.73 94 32.19 23.20

2 Higher than 409.54 and less than or equal to 484.14 63 21.58 25.71

1a Higher than 334.94 and less than or equal to 409.54 15 5.14 20.88

1b 260.54 to less than or equal to 334.94 3 1.03 8.68

Below 1b Less than 260.54 0 0.00 1.48

Table 12.12 Item and respondent classification for each score boundary in financial literacy

Level Score points on the PISA scale Number of items Percentage of items Percentage of respondents

5 Higher than 624.63 22 26.51 9.36

4 Higher than 549.86 and less than or equal to 624.63 14 16.87 17.38

3 Higher than 475.10 and less than or equal to 549.86 24 28.92 24.31

2 Higher than 400.33 and less than or equal to 475.10 12 14.46 22.63

1 Higher than 325.57 and less than or equal to 400.33 6 7.23 15.73

Below 1 Less than 325.57 5 6.02 10.59

Table 12.13 Item and respondent classification for each score boundary in CPS

Level Score points on the PISA scale Number of items Percentage of items Percentage of respondents

4 Higher than 640.00 25 21.37 6.28

3 Higher than 540.00 and less than or equal to 640.00 28 23.93 23.66

2 Higher than 440.00 and less than or equal to 540.00 38 32.48 35.30

1 Higher than 340.00 and less than or equal to 440.00 20 17.09 26.78

Below 1 Less than 340.00 6 5.13 7.99

Page 15: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 239

Because RP62 values and the transformed plausible values are on the same PISA scales, the distribution of respondents’ latent ability and item RP62 values can be located on the same scale. Figures 12.7 to 12.11 illustrate the distribution of the first plausible value (PV1) along with item RP62 values on the PISA scale separately for each cognitive domain for the PISA 2015 main survey data. Note that international RP62 values and international plausible values (PV1) were used for these figures.1 RP62 values for CBA items are denoted on the right side. In each domain, solid circles indicate PBA items and hollow circles indicate additional PBA items from previous PISA cycles that were not administered in PISA 2015 main survey. For the polytomous items where partial scoring was available, only the highest RP62 values are illustrated in these figures. On the left side, the distribution of plausible values is plotted. In each figure, the blue line indicates the empirical density of the plausible values across countries, and the grey line indicates the theoretical normal distribution with mean of plausible values and the variance of plausible values in each domain across countries. Specifically, N(461, 104.172) for mathematics, N(463, 106.832) for reading, N(467, 103.022) for science, N(474, 1232) for financial literacy, and N(483, 101.652) for CPS are displayed as grey lines. (Note that there are RP62 values higher than 1 000 for the CPS domain, these are outside of the region occupied by the vast majority of respondent’s proficiency estimates and therefore are not shown in Figure 12.11.)

Distribution of PV1

Below Level 1

Level 1

Level 2

Level 3

Level 4

Level 5

Level 6

EmpiricalN(461,10851)

Items RP62

0 10 20 30 40 50 60 70 80 90 105 120 135 150 165 180 195

010

020

030

040

050

060

070

080

090

0

PISA 2015 MS (CBA)PISA 2015 MS (PBA)Previous PISA cycles (PBA)

• Figure 12.7 •Item RP62 values and distribution of PV1 in maths

Page 16: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

240 © OECD 2017 PISA 2015 TECHNICAL REPORT

Distribution of PV1

Below Level 1b

Level 1b

Level 1a

Level 2

Level 3

Level 4

Level 5

Level 6

EmpiricalN(463,11413)

Items RP62

0 10 25 40 55 70 85 100 115 130 145 160 175 190 205 220 235

010

020

030

040

050

060

070

080

090

0

PISA 2015 MS (CBA)PISA 2015 MS (PBA)Previous PISA cycles (PBA)

Distribution of PV1

Level 1b

Level 1a

Level 2

Level 3

Level 4

Level 5

Level 6

EmpiricalN(467,10613)

Items RP62

0 15 30 45 60 75 90 105 125 145 165 185 205 225 245 265 285

010

020

030

040

050

060

070

080

090

0

PISA 2015 MS (CBA)PISA 2015 MS (PBA)Previous PISA cycles (PBA)

Below Level 1b

• Figure 12.8 •Item RP62 values and distribution of PV1 in reading

• Figure 12.9 •Item RP62 values and distribution of PV1 in science

Page 17: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 241

Figures 12.12 to 12.16 show the percentage of respondents per country at each level of proficiency for each cognitive domain.

Distribution of PV1

Below Level 1

Level 1

Level 2

Level 3

Level 4

Level 5

EmpiricalN(474,15099)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

010

020

030

040

050

060

070

080

090

0

PISA 2015 MS (CBA)PISA 2015 MS (PBA)Previous PISA cycles (PBA)

Distribution of PV1

Below Level 1

Level 1

Level 2

Level 3

Level 4

EmpiricalN(483,10333)

0 5 10 20 30 40 50 60 70 80 90 100 110

010

020

030

040

050

060

070

080

090

0

PISA 2015 MS (CBA)

• Figure 12.10 •Item RP62 values and distribution of PV1 in financial literacy

• Figure 12.11 •Item RP62 values and distribution of PV1 in collaborative problem solving

Page 18: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

242 © OECD 2017 PISA 2015 TECHNICAL REPORT

22 30 29 27 25 27

29 31 28

31 24

35 24

26 31 29 27

30 24

27 27 25

28 26 24 22 21

24 24

21 22

19 21 19 17 16 17 17 14 16 17 15 15 15 15 14 14 15 14 14 14 15 15 14 12 11 13 12 13 12 10 10 12 11 9

11 10 10

8 8 5 6 6

68 51

49 47

45 44 39

38 38

35 37

27 35 31

26 27

26 24

28 25 25

25 23

23 24

20 21 16 14

15 10 17 12

11 15

12 11

8 15

6 9

7 8 8 9 7 8

9 8 7 5 5

7 8

5 4

4 5

7 4

4 3

5 4

2 5 5 6

3 4

1 3 2

81417161717

21202122

2026

2023

27262526

222524252525

2326

242729

2630

222626

212423

2620

2823252423

222323

2123232626

232124242322

19212222

202021

18171617

15151412

24

56

99

98101012

913

1313

131514

161615161617

1619

1920

2222

2320

2324

222424

2522

2924

282525

242626

242526

2727

2525

2830

2727

2327

2929

2527

2924

2421

2621

2723

20

11

233

23

32

626

534

55

866

766

89

119

912

1114

1315

161716

1617

1618

181818

191819

2119

191918

1920

2121

2121

2222

2423

2323

2423

2322

2623

2927

25

11

1

2

21

111212

21

13

34

323

37

55

777

69

58

688

988

109

877

910

98

910

1210

910

1211

1114

1417

1518

1719

22

1

1

12

11

211

13

12

1223

22

232

22

33

22

33

43

22

34

357

95

105

813Singapore 564

Hong Kong (China) 548Macao (China) 544Chinese Taipei 542

Japan 532 B-S-J-G (China) 531

Korea 524Switzerland 521

Estonia 520Canada 516

Netherlands 512Denmark 511

Finland 511Slovenia 510Belgium 507

Germany 506Poland 504Ireland 504

Norway 502Austria 497

New Zealand 495Viet Nam 495

Russia 494Sweden 494

Australia 494France 493

United Kingdom 492Czech Republic 492

Portugal 492Italy 490

Iceland 488Spain 486

Luxembourg 486Latvia 482Malta 479

Lithuania 478Hungary 477

Slovak Republic 475Israel 470

United States 470Croatia 464

International average 462Kazakhstan 460

Greece 454Malaysia 446Romania 444Bulgaria 441Cyprus1 437

United Arab Emirates 427Chile 423

Turkey 420Moldova 420Uruguay 418

Montenegro 418Trinidad and Tobago 417

Thailand 415Albania 413

CABA (Argentina) 409Mexico 408

Georgia 404Qatar 402

Costa Rica 400Lebanon 396

Colombia 390Peru 387

Indonesia 386Jordan 380Brazil 377

FYROM 371Tunisia 367Kosovo 362Algeria 360

Dominican Republic 328

Below Level 1 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6

2015 PISA main study – mathsAverage scores (PV) & proficiency-level percentages

• Figure 12.12 •Percentage of respondents per country/economy at each level of proficiency for maths

1. Note by Turkey: The information in this document with reference to “Cyprus” relates to the southern part of the Island. There is no single authority representing both Turkish and Greek Cypriot people on the Island. Turkey recognizes the Turkish Republic of Northern Cyprus (TRNC). Until a lasting and equitable solution is found within the context of the United Nations, Turkey shall preserve its position concerning the “Cyprus issue.”Note by all the European Union Member States of the OECD and the European Union: The Republic of Cyprus is recognised by all members of the United Nations with the exception of Turkey. The information in this document relates to the area under the effective control of the Government of the Republic of Cyprus.

Page 19: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 243

Singapore 535Hong Kong (China) 527

Canada 527Finland 526Ireland 521Estonia 519

Korea 517Japan 516

Norway 513New Zealand 509

Germany 509Macao (China) 509

Poland 506Slovenia 505

Netherlands 503Australia 503Sweden 500

Denmark 500France 499

Belgium 499Portugal 498

United Kingdom 498Chinese Taipei 497

United States 497Spain 496

Russia 495B-S-J-G (China) 494

Switzerland 492Latvia 488

Czech Republic 487Croatia 487

Viet Nam 487Austria 485

Italy 485Iceland 482

Luxembourg 481Israel 479

Lithuania 472Hungary 470

Greece 467International average 461

Chile 459Slovak Republic 453

Malta 447Cyprus1 443

Uruguay 437Romania 434

United Arab Emirates 434Bulgaria 432Malaysia 431

Turkey 428Costa Rica 427

Trinidad and Tobago 427Kazakhstan 427

Montenegro 427CABA (Argentina) 425

Colombia 425Mexico 423

Moldova 416Thailand 409

Jordan 408Brazil 407

Albania 405Qatar 402

Georgia 401Peru 398

Indonesia 397Tunisia 361

Dominican Republic 358FYROM 352Algeria 350Kosovo 347

Lebanon 347

Below Level 1b Level 1aLevel 1b Level 2 Level 3 Level 4 Level 5 Level 6

2015 PISA main study – readingAverage scores (PV) & proficiency-level percentages

22 34

37 28

31 34 35

28 26 23

27 27 25

32 25

28 26 26 25

29 22

28 27 25

20 22

23 24

20 17 18 20 18 17 18 17 15 16 14 15 14 12

15 15 13 14 14 13 12 13 12 13 13 13 13 11 12 12 13 11 11 9

11 11 11 9

10 8 8 8 8 7 8

25 28

31 24

28 27

17 19

16 18

16 17

14 15

15 11 14 13 13

11 14

10 11

10 14

13 12 12

11 11 9 7 9

8 8 7 8 8

6 5 7

2 5 6

4 5 6

3 3

5 4

4 4

5 6

3 5 5 4

3 3

2 4 5 4

3 3

2 2 3 2 2

2

24 15

11 19

13 11

4 6

9 11 7

7 7

3 6

2 3 3 4 2 6 2 2

2 8 5 4 3

4 7

4 1

4 2 1

1 3 2

2 1

2

1 1

1 2

1 1

1 1 1

1 2

1 2 1 1

1

1 1

1 1 1

1

16 19

17 19 20 21

31 27

25 23

27 25

31 31

28 34

29 31

29 33

26 35

33 34

22 25

30 28 27

22 26

30 24 25 24 27

22 22

26 25

23 32

27 23

27 23

21 27

24 23 22 24 23

21 19

24 22 21 22 23 22 23

21 21 20 20 19 22 21

18 19 18 17

9 4

4 8 7 7

12 15

16 17

16 16

19 15

19 20

20 20

20 19

20 19

21 23

21 21

21 21 23

22 25

27 24

27 27

27 24 25

27 29

27 35

29 28

32 28

25 31

32 28 31 28 30

27 24

32 27 28 27

30 31

34 28

26 29 30

29 31 32

30 30 32

26

4

2 1 1

2 4 6

7 5

6 4

4 7

4 7 6

8 6

9 5 6

5 12

11 8

9 11

14 14

12 15

16 17

17 19 19

18 19

20 16

19 19

19 21

21 19 22

21 22

20 22

23 23

22 22 22 23

23 23

24 24

22 24

26 25

25 26

28 27

29 27

1

1 1

1 1

1

1 1 1 1

2 1 1

3 3

2 2

3 5

3 2

5 4 4

4 8

7 6

5 6

3 5

7 4

7 9

6 5

8 6

8 7

8 10

6 8 9 9

8 7

6 10

11 10

10 11

10 9

12 12

10 15

1

1

1 1

1 1

1

1 1

1 2

1

1 1

1 1

1 2

1 1 2 1

1 1

2 3

2 1

2 1 1

2 2

1 4

• Figure 12.13 •Percentage of respondents per country/economy at each level of proficiency for reading

1. See note 2 under Table 12.5.

Page 20: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

244 © OECD 2017 PISA 2015 TECHNICAL REPORT

Singapore 556Japan 538

Estonia 534Chinese Taipei 532

Finland 531Macao (China) 529

Canada 528Viet Nam 525

Hong Kong (China) 523B-S-J-G (China) 518

Korea 516New Zealand 513

Slovenia 513Australia 510

United Kingdom 509Germany 509

Netherlands 509Switzerland 506

Ireland 503Belgium 502

Denmark 502Poland 501

Portugal 501Norway 498

United States 496Austria 495France 495

Sweden 493Czech Republic 493

Spain 493Latvia 490

Russia 487Luxembourg 483

Italy 481Hungary 477

Lithuania 475Croatia 475Iceland 473

Israel 467International average 466

Malta 465Slovak Republic 461

Kazakhstan 456Greece 455

Chile 447Bulgaria 446Malaysia 443

United Arab Emirates 437Uruguay 435Romania 435Cyprus1 433

CABA (Argentina) 432Moldova 428

Albania 427Turkey 425

Trinidad and Tobago 425Thailand 421

Costa Rica 420Qatar 418

Colombia 416Mexico 416

Montenegro 411Georgia 411

Jordan 409Indonesia 403

Brazil 401Peru 397

Lebanon 386Tunisia 386

FYROM 384Kosovo 378Algeria 376

Dominican Republic 332

Below Level 1b Level 1aLevel 1b Level 2 Level 3 Level 4 Level 5 Level 6

2015 PISA main study – scienceAverage scores (PV) & proficiency-level percentages

30 43

39 34

44 32

37 32

40 30 31 32

35 33

28 36 34

28 32 30 28 28 27 28 28 26 26

23 25 22 24

20 18

21 20 19 19 19 18 17

19 15 15 14

16 15 15 16 15 14 14 13 13

14 12

14 14 13 14 13 12 13 11 12

8 6

9 7

9 9 8 8 7

40 24

24 22

20 24

19 20

14 15 16

16 12 14

18 10 12

15 12

10 12 10 13 9

11 13

7 12 9

9 4

9 11

9 9

6 5 5 7

5 6

3 3 4

4 6 6 5 4

4 3 3 3

5 3

4 4

4 3 4

3 4

3 4

2

2 1

2 3

1 2 2

16 4

4 7

2 7

3 4

1 4

4 3

1 2 4

1 1

3 1

2 2

1 2

1 1 3

3 1

1

2 4 2 2

1

1 1

1

1 1

1

1

1

1

1123242527

2228

253231

2829

3531

2535

3227

3135

3134

2935

3027

3625

3128

3828

232624

292930

2527

253130

2726

2422242525252726

2226

232223232223

22222120

252021191820

1815

36

7107

1211

1311

161515

1516

1615

1618

1919

2020

2020

2019

2423

2425

2425

2223

23272826

2729

2531

3231

2827

2628272929

3031

2731

2626

2828

2729

2629

2636

3730

3429

2731

2823

11

213

24

23

54

24

83

57

54

65

86

79

611

912

813

151415

151415

1717

171617

1918

1921

2019

2021

2020

2220

2322

2222

2222

2224

2427

2426

2826

2727

2928

1

1

2

1

11

11

13

13

12

23

655

344

44

643

56

7777

7766

86

99

999

910

911

77

108

1213

1213

19

211

1

11111

1111

11

12222

23

12

12

12

32

26

• Figure 12.14 •Percentage of respondents per country/economy at each level of proficiency for science

1. See note 2 under Table 12.5.

Page 21: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 245

B-S-J-G (China) 566

Belgium 541

Canada 533

Russia 512

Netherlands 509

Australia 504

United States 487

Poland 485

Italy 483

International average 481

Spain 469

Lithuania 449

Slovak Republic 445

Chile 432

Peru 403

Brazil 393

Below Level 1 Level 1 Level 2 Level 3 Level 4 Level 5

2015 PISA main study – financial literacyLiteracy average scores (PV) & proficiency-level percentages

24

24

22

18

19

16

15

14

14

15

12

12

9

8

8

6

29

24

16

16

12

9

10

6

6

7

8

7

2

4

4

3

22

26

26

24

27

26

22

25

24

23

19

18

23

17

15

13

15

18

22

22

25

27

24

29

28

26

24

23

32

25

22

20

7

7

10

13

13

16

18

19

19

19

22

22

24

24

27

24

3

1

3

6

4

6

11

6

8

10

15

17

11

22

24

33

• Figure 12.15 •Percentage of respondents per country/economy at each level of proficiency for financial literacy

Note: The financial literacy data from Belgium come from the Flanders part of Belgium only and thus are not nationally representative; the same is the case with regard to the financial literacy data from Canada since some provinces of Canada did not participate in the financial literacy assessment.

Page 22: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

246 © OECD 2017 PISA 2015 TECHNICAL REPORT

Singapore 561Japan 552

Hong Kong (China) 541Korea 538

Canada 535Estonia 535Finland 534

Macao (China) 534New Zealand 533

Australia 531Chinese Taipei 527

Germany 525United States 520

Denmark 520United Kingdom 519

Netherlands 518Sweden 510Austria 509

Norway 502Slovenia 502Belgium 501Iceland 499

Czech Republic 499Portugal 498

Spain 496B-S-J-G (China) 496

France 494Luxembourg 491

International average 486Latvia 485

Italy 478Russia 473

Croatia 473Hungary 472

Israel 469Lithuania 467

Slovak Republic 463Greece 459

Chile 457Cyprus1 444Bulgaria 444Uruguay 443

Costa Rica 441Malaysia 440Thailand 436

United Arab Emirates 435Mexico 433

Colombia 429Turkey 422

Peru 418Montenegro 416

Brazil 412Tunisia 382

Below Level 1 Level 1 Level 2 Level 3 Level 4

2015 PISA main study – CPSAverage scores (PV) & proficiency-level percentages

60 43

45 43 45 42 41

38 42 39 41 38

34 36 34 32 31 30 30 29 29 29 27 25 26 25 23 22 21 22 22 23 21 21 21 20 20 19 18 16

19 17 14 16 16

13 15 13

15 11 12

9 10

25 21 18 18 15

14 12

16 12

11 9 13

15 13

8 10 10

8 12

9 7

7 8

6 8

7 7 6

4 5 5

5 6 4 4 5 5

3 4

3 5

4 3

4 4

2 3

2 3

1 2

1 2

15 28

32 31 34 34

37 32 35

40 40

34 33 36

40 38 38 39

31 37

42 40 38 41

35 36 36 38

42 40 40

38 37 39 39

36 36 36 35

39 33 34 37

31 31

36 32 35

32 35

34 31

28

17

68

79

913

101010

1416

1416

181820

2222

202023

2424

262827

282829

2829

2928

303032

3133

3032

363433

3835

3734

424044

39

1

1

21

1222

123

25

32

44

47

776

455

77679910

129

1413

101516

1114

1216

1013

1421

• Figure 12.16 •Percentage of respondents per country/economy at each level of proficiency for CPS

Note: The CPS sample from Israel does not include ultra-Orthodox students and thus is not nationally representative. 1. See note 2 under Table 12.5.

Domain inter-correlationsEstimated correlations between the PISA domains, based on the 10 plausible values and averaged across all countries and assessment modes, are presented in Table 12.14. Overall, the correlations are quite high, as expected, yet there is still some separation between each of the domains. The estimated correlations at the national level are presented in Table 12.15.

Page 23: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 247

Table 12.14 Domain inter-correlations1

Domain Reading Science CPS Financial literacy

Maths

Average 0.79 0.88 0.70 0.74

Average (CBA) 0.79 0.88 0.70 0.74

Average (PBA) 0.75 0.80 – –

Range 0.57~0.87 0.70~0.91 0.55~0.76 0.60~0.81

Reading

Average

0.87 0.74 0.75

Average (CBA) 0.87 0.74 0.75

Average (PBA) 0.77 – –

Range 0.71~0.90 0.58~0.80 0.61~0.81

Science

Average

– –

0.77 0.77

Average (CBA) 0.77 0.77

Average (PBA) – –

Range 0.65~0.83 0.68~0.85

CPS

Average

– – –

0.64

Average (CBA) 0.64

Average (PBA) –

Range 0.50~0.71

1. Please note that Argentina, Malaysia and Kazakhstan were not included in this analysis due to adjudication issues (inadequate coverage of either population or construct).

Table 12.15[Part 1/2]National-level domain inter-correlations based on 10 PVs

Country/economyMaths &reading

Maths &science

Maths & CPS

Maths &fin. lit.

Reading &science

Reading &CPS

Reading &fin. lit.

Science &CPS

Science &fin. lit.

CPS & fin. lit.

Albania 0.68 0.80 – – 0.77 – – – – –

Algeria 0.57 0.70 – – 0.71 – – – – –

Argentina 0.75 0.83 – – 0.81 – – – – –

Australia 0.79 0.88 0.68 0.79 0.87 0.75 0.8 0.76 0.85 0.7

Austria 0.80 0.89 0.71 – 0.88 0.77 – 0.78 – –

B-S-J-G (China) 0.84 0.91 0.76 0.80 0.90 0.76 0.80 0.80 0.83 0.70

Belgium 0.84 0.90 0.73 0.80 0.90 0.76 0.80 0.78 0.83 0.67

Brazil 0.75 0.84 0.65 0.62 0.86 0.73 0.65 0.75 0.68 0.54

Bulgaria 0.80 0.89 0.74 – 0.89 0.80 – 0.83 – –

Canada 0.77 0.87 0.67 0.68 0.87 0.74 0.70 0.75 0.74 0.59

Chile 0.80 0.88 0.70 0.75 0.87 0.74 0.75 0.77 0.78 0.64

Colombia 0.83 0.90 0.74 – 0.90 0.74 – 0.80 – –

Costa Rica 0.75 0.83 0.59 – 0.85 0.67 – 0.68 – –

Croatia 0.80 0.89 0.69 – 0.87 0.75 – 0.76 – –

Cyprus1 0.74 0.85 0.65 – 0.83 0.71 – 0.74 – –

Czech Republic 0.84 0.90 0.69 – 0.89 0.72 – 0.75 – –

Denmark 0.77 0.87 0.69 – 0.86 0.72 – 0.77 – –

Dominican Republic 0.78 0.83 – – 0.85 – – – – –

Estonia 0.78 0.88 0.71 – 0.87 0.74 – 0.79 – –

Finland 0.79 0.87 0.72 – 0.87 0.75 – 0.78 – –

France 0.84 0.91 0.70 – 0.90 0.75 – 0.78 – –

FYROM 0.75 0.78 – – 0.74 – – – – –

Georgia 0.79 0.79 – – 0.73 – – – – –

Germany 0.81 0.90 0.70 – 0.88 0.72 – 0.77 – –

Greece 0.79 0.88 0.73 – 0.88 0.75 – 0.79 – –

Hong Kong 0.77 0.88 0.64 – 0.86 0.73 – 0.74 – –

Hungary 0.83 0.90 0.74 – 0.90 0.78 – 0.81 – –

Iceland 0.78 0.86 0.70 – 0.84 0.74 – 0.76 – –

Indonesia 0.70 0.82 – – 0.75 – – – – –

Ireland 0.81 0.89 – – 0.88 – – – – –

Israel 0.83 0.89 0.75 – 0.89 0.78 – 0.80 – –

Page 24: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

248 © OECD 2017 PISA 2015 TECHNICAL REPORT

Table 12.15[Part 2/2]National-level domain inter-correlations based on 10 PVs

CountriesMaths &Reading

Maths &Science

Maths & CPS

Maths &Fin. Lit.

Reading &Science

Reading &CPS

Reading &Fin. Lit.

Science &CPS

Science &Fin. Lit.

CPS & Fin. Lit.

Italy 0.75 0.85 0.65 0.68 0.84 0.68 0.67 0.73 0.73 0.56

Japan 0.79 0.87 0.66 – 0.86 0.73 – 0.72 – –

Jordan 0.70 0.79 – – 0.78 – – – – –

Kazakhstan 0.61 0.73 – – 0.70 – – – – –

Korea 0.78 0.87 0.72 – 0.85 0.76 – 0.77 – –

Kosovo 0.74 0.81 – – 0.78 – – – – –

Latvia 0.77 0.87 0.66 – 0.87 0.73 – 0.75 – –

Lebanon 0.80 0.82 – – 0.81 – – – – –

Lithuania 0.79 0.90 0.72 0.70 0.87 0.74 0.73 0.79 0.75 0.63

Luxembourg 0.83 0.91 0.73 – 0.90 0.78 – 0.78 – –

Macao 0.75 0.84 0.65 – 0.89 0.78 – 0.78 – –

Malaysia 0.78 0.87 0.72 – 0.88 0.74 – 0.79 – –

Malta 0.83 0.87 – – 0.87 – – – – –

Mexico 0.77 0.84 0.67 – 0.86 0.73 – 0.76 – –

Moldova 0.73 0.79 – – 0.77 – – – – –

Montenegro 0.76 0.83 0.66 – 0.84 0.70 – 0.74 – –

Netherlands 0.87 0.91 0.75 0.81 0.89 0.78 0.81 0.77 0.84 0.70

New Zealand 0.79 0.89 0.70 – 0.87 0.75 – 0.78 – –

Norway 0.78 0.89 0.68 – 0.84 0.72 – 0.74 – –

Peru 0.81 0.86 0.73 0.76 0.88 0.78 0.81 0.79 0.79 0.70

Poland 0.80 0.90 – 0.74 0.86 – 0.75 – 0.77 –

Portugal 0.79 0.89 0.70 – 0.86 0.74 – 0.76 – –

Qatar 0.84 0.88 – – 0.90 – – – – –

Romania 0.79 0.78 – – 0.77 – – – – –

Russian Federation 0.66 0.82 0.55 0.60 0.81 0.68 0.61 0.70 0.68 0.50

Singapore 0.82 0.89 0.73 – 0.90 0.78 – 0.80 – –

Slovak Republic 0.83 0.88 0.69 0.66 0.87 0.74 0.66 0.74 0.68 0.58

Slovenia 0.79 0.89 0.68 – 0.87 0.73 – 0.74 – –

Spain 0.76 0.88 0.66 0.71 0.86 0.71 0.72 0.74 0.75 0.61

Sweden 0.78 0.89 0.71 – 0.85 0.78 – 0.77 – –

Switzerland 0.81 0.88 – – 0.88 – – – – –

Chinese Taipei 0.83 0.90 0.71 – 0.90 0.77 – 0.77 – –

Thailand 0.75 0.83 0.65 – 0.87 0.76 – 0.78 – –

Trinidad and Tobago 0.81 0.87 – – 0.80 – – – – –

Tunisia 0.72 0.81 0.59 – 0.83 0.58 – 0.65 – –

Turkey 0.76 0.86 0.68 – 0.85 0.71 – 0.76 – –

United Arab Emirates 0.81 0.88 0.74 – 0.89 0.80 – 0.81 – –

United Kingdom 0.77 0.87 0.68 – 0.86 0.74 – 0.76 – –

United States 0.83 0.90 0.76 0.80 0.90 0.79 0.80 0.82 0.83 0.71

Uruguay 0.79 0.88 0.71 – 0.87 0.73 – 0.77 – –

Viet Nam 0.81 0.87 – – 0.85 – – – – –

1. See note 2 under Table 12.5.

Science scale and subscalesThe estimated correlations between the PISA 2015 science subscales and the domains of reading, mathematics, science and financial literacy scales, are presented in Tables 12.16 to 12.18. The different science subscales, which belong to the three scales or subscale groups Knowledge (SKCO, SKPE), Competency (SCEP, SCED, SCID), and System (SSPH, SSLI, SSES), were considered.

Please note that because of the way in which the proficiency data were generated, you should not calculate the correlations among the knowledge, competency and systems subscales. Therefore these are presented in separate tables.

Page 25: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

PISA 2015 TECHNICAL REPORT © OECD 2017 249

Table 12.16 Estimated correlations among domains and science knowledge subscales1

Reading Science CPS Financial literacy SKCO SKPE

Maths 0.783 0.863 0.692 0.726 0.798 0.808

Reading 0.853 0.741 0.738 0.786 0.817

Science 0.765 0.770 – –

CPS 0.630 0.688 0.722

FinLit 0.743 0.763

SKCO 0.921

Note: Content, SKPE: Procedural & Epistemic.1. Please note that Argentina, Malaysia and Kazakhstan were not included in this analysis due to adjudication issues (inadequate coverage of either population or construct).

Table 12.17 Estimated correlations among domains and science Competency subscales1

Reading Science CPS Financial literacy SCED SCEP SCID

Maths 0.783 0.863 0.692 0.726 0.778 0.797 0.802

Reading 0.853 0.741 0.738 0.790 0.786 0.805

Science 0.765 0.770 – – –

CPS 0.630 0.700 0.687 0.712

FinLit 0.733 0.743 0.756

SCED 0.894 0.903

SCEP 0.919

Note: SCED: Evaluate and Design Scientific Inquiry, SCEP: Subscale of Science Explain Phenomena Scientifically, SCID: Interpret Data and Evidence Scientifically.1. Please note that Argentina, Malaysia and Kazakhstan were not included in this analysis due to adjudication issues (inadequate coverage of either population or construct).

Table 12.18 Estimated correlations among domains and science System subscales1

Reading Science CPS Financial literacy SSES SSLI SSPH

Maths 0.783 0.863 0.692 0.726 0.791 0.798 0.791

Reading 0.853 0.741 0.738 0.791 0.804 0.781

Science 0.765 0.770 --- --- ---

CPS 0.630 0.693 0.711 0.688

FinLit 0.743 0.754 0.736

SSES 0.910 0.900

SSLI 0.908

Note: SSPH: Physical, SSLI: Living, SSES: Earth & Science.1. Please note that Argentina, Malaysia and Kazakhstan were not included in this analysis due to adjudication issues (inadequate coverage of either population or construct).

Page 26: 12 Scaling outcomes - OECD...by-country cells through the total item-by-country cells. Note that the percentage of scalar/metric invariant international/ common item parameters was

12SCALING OUTCOMES

250 © OECD 2017 PISA 2015 TECHNICAL REPORT

Note

1. Please note that Argentina, Malaysia and Kazakhstan were not included in this analysis due to adjudication issues (inadequate coverage of either population or construct).

References

Efron, B. (1982), “The Jackknife, the Bootstrap, and Other Resampling Plans”, Society of Industrial and Applied Mathematics CBMS-NSF Monographs, Vol. 38.

Hoaglin, D.C., F. Mosteller and J.W. Tukey, (1983), Understanding Robust and Exploratory Data Analysis, John Wiley & Sons, New York, NY.

Mislevy, R.J. and K.M. Sheehan, (1987), “Marginal estimation procedures”, in A.E. Beaton (Ed.), Implementing the new design: The NAEP 1983-84 technical report, (Report No. 15-TR-20), Educational Testing Service, Princeton, NJ.

OECD (2002), Reading for Change: Performance and Engagement across Countries: Results from PISA 2000, OECD Publishing, Paris, http://dx.doi.org/10.1787/9789264099289-en.

von Davier et al. (2006), “The statistical procedures used in National Assessment of Educational Progress: Recent developments and future directions”, in C.R. Rao and S. Sinharay (Ed.), Handbook of Statistics,Vol. 26, pp. 1039-1055, Elsevier.