evaluation of internal migration data collected from population censuses

United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011

Evaluation of Internal Migration Data Collected from Population Censuses

United Nations Statistics Division


Outline

- Related concepts of internal migration

- Direct and indirect estimates of internal migration

- Sample tabulations

- Discussion on quality issues


Internal migration – related concepts

- Mobility versus migration

- Migration refers to “long-distance” move, i.e., moves across states or county lines (usually referring to across administrative unit borders)

- Migration change of place of usual residence

- Time element

- Geographic moves


Internal migration – related conceptshort and long distance moves

Data source: Methods and Materials of Demography, classification based on “1-year” data from the March 2000 Current Population Survey of the US


Place of usual residence (UN, 2008)It is recommended that countries apply a threshold of 12 months when considering place

of usual residence according to one of the following two criteria:

(a) The place at which the person has lived continuously for most of the last 12 months (that is, for at least six months and one day), not including temporary absences for holidays or work assignments, or intends to live for at least six months;

(b) The place at which the person has lived continuously for at least the last 12 months, not including temporary absences for holidays or work assignments, or intends to live for at least 12 months.

Difficult to treat groups:- Seasonal residence- work in one place during weekdays and join family member during weekends- College students

Internal migration – related concepts (2)


Internal migration – related concepts (3)

Lifetime migration:

- Migration occurred between birth and the time of the census

Recent migration:

- Migration occurred in recent period, e.g., 1 year


Internal migration data from censuses

- Tabulated from direct questions about mobility or about prior residence- Place of birth- Place of residence at a fixed past date- Duration of residence- Previous place of residence

- Estimates of net migration derived from (residual estimates)- Counts of total population or population disaggregated by age and

sex, at two censuses- Natural increase or intercensal survival rates, which are derived in

turn from (a) life tables or (b) comparison of the age distributions of countries not experiencing immigration or emigration in successive censuses


Internal migration data from censuses – direct method

- Place of birth- Civil division of birth for native-borns; usually refers to the geographical unit of the

country in which the mother resides at the time of the person’s birth- Country if foreign-born

- Place of residence at a specified date in the past- Major or smaller division, or a foreign country- 1 or 5 years, or both- 1 year easier to recall- Different date may be used depends on national circumstances

- Duration of residence- Should refer to the length of residence in the major or smaller civil divisions and the

locality, but not in the particular housing unit

- Place of previous residence- Major or smaller division, or a foreign country


Internal migration data from censuses – direct methodplace of birth (1)

Source: The Methods and Materials of Demography, 2nd edition, Siegel and Swanson, 2004



Source: The Methods and Materials of Demography, 2nd edition, Siegel and Swanson, 2004


Intercensal migration can be estimated by using data by place of birth from two consecutive censuses

Net migration for an area M = (It+n-Ot+n) – (S1It – S2Ot )

It: life time in-migrants at time t

It+n: life time in-migrants at time t+n

Ot: life time out-migrants at time t

Ot+n: life time out-migrants at time t+n

S1: proportion of life time in-migrants It that will survive to time t+n

S2: proportion of life time out-migrants t that will survive to time t+n




Source: Manual VI: Methods of Measuring Internal Migration, United Nations, 1970



Quality issues:

- Memory problem

- Uncertainties about area boundaries at the time of birth

- Errors in reporting of birthplaces for babies who were not born at the usual residence of their parents

- Reporting birthplace according to the old administrative boundaries

- Reporting place of births like hospitals rather than place of usual residence of the mother


Internal migration data from censuses – direct method place of birth (6)

Ways to assess data quality:

- re-interviews or matching studies of a sample of the original records (US census Bureau, 1995, p.19)

- Study the impact of boundary changes:

- Lee et al. 1957

- Compare between censuses or with household surveys


Internal migration data from censuses – direct methodresidence at a fixed past date (1)

Source: Statistics Bureau of Japan



Information may be used to get a sense of “flow”: annual in-migrants and out-migrants for different areas.



Quality issues:

- Memory problem, the longer the period used, the less accurate the information is

- Mis-reporting of previous residence

- Change of boundaries


Internal migration data from censuses – direct methodduration of residence + previous residence (1)

Distribution of lifetime migrants by duration of stay in each State



Internal migration data from censuses – direct method duration of residence + previous residence (2)

For recent migrants: longer distance more migrants




Origin, destination and time of migration (duration):




Quality issues:

- Memory problem, might not remember when moved

- Digit preference (similar to those reflected in age-reporting)


Internal migration data from censuses – indirect method National growth rate method (1)

• National growth rate method – for net internal migration

001001 /)(/)( tttiiii PPPPPPm Population of area i in the first census

Population of area i in the second census

Total population of a country in the first census

Total population of a country in the first census

0iP

1

0

1

t

t

i

P

P

P

Positive rate: with net inmigration; negative rate: net outmigration Assumes same natural increase rate and net immigration from abroad for

all parts of the country


• National growth rate method – example

Population

Rate of Net Internal Migration2001 1991

Austria: Burgenland 277569 270880 -0.0057

Austria: Corinthia 559404 547798 -0.0092

Austria: Lower Austria 1545804 1473813 0.0184

Austria: Salzburg 515327 482365 0.0379

Austria: Styria 1183303 1184720 -0.0316

Austria: Tirol 673504 631410 0.0363

Austria: Upper Austria 1376797 1333480 0.0021

Austria: Vienne 1550123 1539848 -0.0237

Austria: Vorarlberg 351095 331472 0.0288

Austria: Total 8032926 7795786

Internal migration data from censuses – indirect method National growth rate method (2)

Data source: graph produced based on data from United Nations Demographic Yearbook


Vital statistics method for net migration rate 0001 /)(/)( tttiiii PDBPPPm

Births nationally during the intercensal period

Deaths nationally during the intercensal periodt

t

D

B

Assumes same natural increase rate across all areas

Calculate net migration rate (incl. both internal and international migration)

Internal migration data from censuses – indirect method Vital statistics method (1)


Population

Rate of net migration2001 1991

Austria: Burgenland 277569 270880 0.0159

Austria: Corinthia 559404 547798 0.0124

Austria: Lower Austria 1545804 1473813 0.0401

Austria: Salzburg 515327 482365 0.0596

Austria: Styria 1183303 1184720 -0.0100

Austria: Tirol 673504 631410 0.0579

Austria: Upper Austria 1376797 1333480 0.0237

Austria: Vienne 1550123 1539848 -0.0021

Austria: Vorarlberg 351095 331472 0.0504

Austria: Total 8032926 7795786

Vital statistics method – example

Internal migration data from censuses – indirect method Vital statistics method (2)

Data source: graph produced based on data from United Nations Demographic Yearbook


Survival-rate method

ssPPM xt

txtx

x )( 0

Net migration for the cohort aged x at year 0 to year t

Population size for cohort x (at year 0) at year t

Survival rate of the cohort from year 0 to year t

Population size for cohort x at year 0

Adjustment for deaths of migrants during the periods

P

s

P

M

x

ttx

txx

0

s can be calculated by x

xL

L5

105

Internal migration data from censuses – indirect method Survival rate method (1)


Internal migration data from censuses – indirect methodSurvival rate method (2): Vienna, Austria

AgePopulation in

199110-year life table

survival ratio Age Population in 2001 expected survivors Net migration

(1) (2) (3) (4) (5) (6) = (2)*(3) (7) = (5) - (6)

0 - 4 39,766 0.99622529 10 - 14 38,867 39616 -749

5 - 9 36,574 0.991467948 15 - 19 38,979 36262 2,717

10 - 14 34,289 0.988364131 20 - 24 42,705 33890 8,815

15 - 19 40,166 0.987782981 25 - 29 54,108 39675 14,433

20 - 24 62,313 0.985758641 30 - 34 69,222 61426 7,796

25 - 29 72,289 0.980066411 35 - 39 71,228 70848 380

30 - 34 62,655 0.969033736 40 - 44 59,845 60715 -870

35 - 39 51,290 0.951866079 45 - 49 49,023 48821 202

40 - 44 56,236 0.927062515 50 - 54 51,774 52134 -360

45 - 49 56,240 0.886929277 55 - 59 49,495 49881 -386

50 - 54 48,941 0.826409977 60 - 64 41,373 40445 928

55 - 59 32,213 0.749135574 65 - 69 25,381 24132 1,249

60 - 64 33,819 0.639850773 70 - 74 24,730 21639 3,091

65 - 69 30,831 0.488011131 75 - 79 19,593 15046 4,547

70 - 74 19,021 0.399270089 80 - 84 9,472 7595 1,877

75 - 79 18,050 0.33555271 85 - 89 5,486 6057 -571

80 + 19,832 0.204715764 90+ 2,336 4060 -1,724

All ages 714,525 Total 10+ 653,617 612241 41376

Tabulated based on data obtained from Austria Statistics Office online database


Possible concerns/errors to use indirect method

• Change of area boundaries

• Mixture with international migration

• Depends on errors in all components:

• Population by age and sex

• Births

• Deaths

evaluation of internal migration data collected from population censuses

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