AnthropometryTechnique of measuring people

MeasureIndexIndicatorReferenceInformation

MeasurementsWeight Height Length and stature or heightMid Upper Arm Circumference MUAC

Characteristics we need: easycheapacceptablereproducible

INDEXRelation between two measurementsweight for age W/A or W//A general appreciation of nutritional statusheight for age H/A or H//A measure of linear growth deficit or STUNTINGweight for height/length W/H or W//H measure of weight deficit according to length WASTING

WEIGHTSensitive to changesChanges in two directions up and downFast changeUsually easy to collectStandardisation of scales needed, calibrationSmall changes are difficult to measure: food intake of the child, urine, dehydration, temp, etc: not very specificcommunity aversion: connotationscan be difficult: co-operation of childrento nearest 100 gr.

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HeightDifficult to measure, accuracy, large variationsDifferences are small: 24 cm increment in the first year of life, 11 cm second year, 8 thirdLow sensitivityLarge measurement errorsStunted versus stuntingstunted is a heterogeneous groupstunting is the active process: determinants are actingMeasure to the nearest mmBelow 2 recumbent, above standing

AGEUsually the most difficult and inaccurate measurementLess of a problem if a trend in the same child is measured, the mistake is repeated every time and thus cancels out

Growth of a child

IndicatorPartial quantification of a conceptpartialquantificationconceptnumber or percent of defined group below a cut-off valuecut-off : z-scores, -2 and +2 , 95% of populationz-score = X-Mean / SDbelow -2 in normal distribution 2.27 % !!Percentages: value = % of the meanpercentiles: range from 1 to 100

The referenceOne reference for all??Reference or standard?Genetic differencesDo they existAre they importantReference means operational decisions

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

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Age in years

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Height in centimetre

Belgium (1)

Britain (2)

Cambridge (3)

NCHS (4)

Criteria for a reference1.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.

COMMON ERRORSFirst year of life is up to 11.9 months of age and not O-12Length and height; change technique at 24 mo Percentage and z-score80% is -1.5 Z-score at 6 mo and -2 Z score at 2 yrsLack of distinction between descriptive use and operational useNo use of statistics: Confidence intervals and tests to compare prevalence and averagesUndernutrition Wasting Stunting

Classifications: GOMEZ

PRIVATE 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

PRIVATE Waterlow

Weight for

Height

Classification

>= 80 %

< 80 %

Height for

>= 90 %

Normal

Wasted

Age

< 90 %

Stunted

Wasted and stunted

Anthropometry is an operational toolIdentification 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.

Se and Sp Truly MalnourishedYesNoDiagnosed asYesTPFPmalnourishedNoFNTN

TP= true positiveFP= false positiveTN= true negativeFN= false negative

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

Disease +

Disease -

Test +

TP

(Se*P)

FP

(1-Sp)*(1-P)

Test -

FN ((1-Se)*P)

TN ( Sp*(1-P))

P= prevalence

1-P

reformulationPPV= TP /TP +FPPPV= Se*P / (Se*P) + ((1-Sp) * (1-P))

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

Disease +

Disease -

Test +

TP

(Se*P)

FP

(1-Sp)*(1-P)

Test -

FN ((1-Se)*P)

TN( Sp*(1-P))

P= prevalence

1-P

Use of AnthropometryIndividual 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

IndicesW/A: combined measurement:NO individual diagnosis but trend assessmentFor growth monitoring and FU W/H indicates degree of wastingIndividual diagnosisCommunity diagnosisSensitive to changeH/A indicates linear growth retardationnot sensitive to changeslow progressCommunity diagnosisALL complex causality

Summary of applications

IndexApplication

Indicator

ACEmergencies (screening)CUa flexible

W/HEmergencies (screening)CUa flexible

One time assessment ofMean (SD) or

wastingConventional CU

Assessment of impact ofMean (SD)

short term programmeConventional CU

Rapid targeting andConventional CU

early warning

Growth monitoringNone

W/AGrowth monitoringNone

H/ALong-term planningMean (SD)

Surveillance of trendsMean (SD)

(long term)

Programme managementMean(SD)

growth monitoringNone

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