anthropometry technique of measuring people measure index indicator reference information

Anthropometry

• Technique of measuring people

Measure

Index

Indicator

Reference

Information

Measurements

• Weight • Height • Length and stature or height• Mid Upper Arm Circumference MUAC

Characteristics we need: » easy

» cheap

» acceptable

» reproducible

• Relation between two measurements• weight for age W/A or W//A general appreciation

of nutritional status• height for age H/A or H//A measure of linear

growth deficit or STUNTING• weight for height/length W/H or W//H measure of

weight deficit according to length WASTING

INDEX

• Sensitive to changes• Changes in two directions up and down• Fast change• Usually easy to collect• Standardisation of scales needed, calibration• Small changes are difficult to measure: food intake

of the child, urine, dehydration, temp, etc: not very specific

• community aversion: connotations• can be difficult: co-operation of children• to nearest 100 gr.

WEIGHT

• Difficult to measure, accuracy, large variations• Differences are small: 24 cm increment in the first

year of life, 11 cm second year, 8 third• Low sensitivity• Large measurement errors• Stunted versus stunting

– stunted is a heterogeneous group

– stunting is the active process: determinants are acting

• Measure to the nearest mm• Below 2 recumbent, above standing

Height

• Usually the most difficult and inaccurate measurement

• Less of a problem if a trend in the same child is measured, the mistake is repeated every time and thus cancels out

AGE

Growth of a child

• Partial quantification of a concept– partial– quantification– concept

• number or percent of defined group below a cut-off value

• cut-off : z-scores, -2 and +2 , 95% of population• z-score = X-Mean / SD• below -2 in normal distribution 2.27 % !!• Percentages: value = % of the mean• percentiles: range from 1 to 100

Indicator

• One reference for all??• Reference or standard?• Genetic differences

– Do they exist

– Are they important

• Reference means operational decisions

The reference

Secular trends in height of 9- and 11-year-old schoolboys in Japan

118

120

122

124

126

128

130

132

134

136

138

1900 1910 1920 1930 1940 1950 1960

Hei

ght (

cm)

11 years old boys

9 years old boys

Figure 2.1. Attained height of early 19th century boys compared to NCHS reference data

(1) Boys from Brussels, Nivelles and Leuven n = 700 /age group(2) Factory workers from Stockfort and Manchester n: not quoted(3) University students from Cambridge at entry at Universty n = 80 (4) NCHS median

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Age in years

0

50

100

150

200Height in centimetre

Belgium (1) Britain (2) Cambridge (3) NCHS (4)

• 1. Measurements should relate to a well-nourished population.

• 2. Sample : at least 200 individuals in each age and sex group.

• 3. Sample: cross-sectional, since the comparisons that will be made are of a cross-sectional nature.

• 4. Sampling procedures should be defined and reproducible.

• 5. Measurements should be carefully made and recorded by observers trained in anthropometric techniques, using equipment of well tested design and calibrated at frequent intervals.

• 6. The measurements made on the sample should include all the anthropometric variables that will be used in the evaluation of nutritional status.

• 7. The data from which reference graphs and tables are prepared should be available for anyone wishing to use them, and the procedures used for smoothing curves and preparing tables should be adequately described and documented.

Criteria for a reference

• First year of life is up to 11.9 months of age and not O-12

• Length and height; change technique at 24 mo • Percentage and z-score

– 80% is -1.5 Z-score at 6 mo and -2 Z score at 2 yrs

• Lack of distinction between descriptive use and operational use

• No use of statistics: Confidence intervals and tests to compare prevalence and averages

• Undernutrition Wasting Stunting

COMMON ERRORS

Classifications: GOMEZ

Percentage W/A TYPE

>= 90 % Normal

75 - 90 % First degree / mild malnutrition

60 - 74 % Second degree / moderate malnutrition

< 60 % Third degree / severe malnutrition

Classifications: WATERLOW

Waterlow Weight for Height

Classification >= 80 % < 80 %

Height for >= 90 % Normal Wasted

Age < 90 % Stunted Wasted and stunted

• Identification serve a purpose , the identified should be dealt with. Capacity of numbers.

• Sensitivity (Se) is the ability of a test to identify as positive those who are diseased.

• Specificity (Sp) is the ability of a test to identify as negative those who are healthy.

• Positive predictive value: If you test positive, what is the chance of really being positive.

• Negative predictive value is the chance of being healthy whilst being identified as negative. The chance of being really negative is higher when there are no false negatives, i.e. when the sensitivity is higher.

Anthropometry is an operational tool

Truly MalnourishedYes No

Diagnosed as Yes TP FPmalnourished No FN TN

• TP= true positive• FP= false positive• TN= true negative• FN= false negative

• Se= TP/(TP+FN)• Sp= TN/(TN+FP)• Positive predictive value (PPV) = TP/(TP+FP)• Negative predictive value (NPV) = TN/(TN+FN)

Se and Sp

Disease + Disease -

Test + TP (Se*P) FP (1-Sp)*(1-P)

Test - FN ((1-Se)*P) TN ( Sp*(1-P))

P= prevalence 1-P

PPV= TP /TP +FP

PPV= Se*P / (Se*P) + ((1-Sp) * (1-P))

NPP= TN/FN + TN

NPP= Sp(1-P) / (Sp * (1-P) + ((1-Se) * P)

reformulation

Disease + Disease -

Test + TP (Se*P) FP (1-Sp)*(1-P)

Test - FN ((1-Se)*P) TN( Sp*(1-P))

P= prevalence 1-P

Individual Level SCREENING: ONE TIME ASSESSMENT

to immediately decrease case fatality (emergency situations)

in non-emergency situations

GROWTH MONITORING: TREND ASSESSMENT Population Level

ONE TIME ASSESSMENT under circumstances of food crisis for long-term planning

NUTRITIONAL SURVEILLANCE: TREND ASSESSMENT for long-term planning for timely warning for programme management

Use of Anthropometry

• W/A: combined measurement:– NO individual diagnosis but trend assessment– For growth monitoring and FU

• W/H indicates degree of wasting– Individual diagnosis– Community diagnosis– Sensitive to change

• H/A indicates linear growth retardation– not sensitive to change– slow progress– Community diagnosis

• ALL complex causality

Indices

Index Application Indicator

AC Emergencies (screening) CUa flexible

W/H Emergencies (screening) CUa flexibleOne time assessment of Mean (SD) orwasting Conventional CUAssessment of impact of Mean (SD)short term programme Conventional CURapid targeting and Conventional CU early warningGrowth monitoring None

W/A Growth monitoring None

H/A Long-term planning Mean (SD)Surveillance of trends Mean (SD)(long term)Programme management Mean(SD)growth monitoring None

a CU = Cut-off, conventional CU = - 2SD.

Summary of applications