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For surviving children born in the three to five years before the survey, HWBMIZWHO (HW73) reports the difference between the child's body mass index (BMI) and the median BMI of a reference population of the same age and sex, expressed in units equal to one standard deviation of the reference population's distribution. An anthropometry measure expressed in reference standard deviation units is also known as a Z-score. HWBMIZWHO values are reported in units equal to 100 times the Z-score, to preserve two decimal places without requiring the use of a decimal point. Dividing HWBMIZWHO by 100 will yield a child's BMI-for-age Z-score (BMIZ) value.

BMI is an anthropometric measure relating weight to height, equal to body weight (kilograms) divided by height (meters) squared. Considered in relation to a reference population, child BMI-for-age is valuable for assessing either underweight or overweight status, and particularly useful in settings where child malnutrition and child obesity coexist.

Reference populations used to generate HWBMIZWHO draw from the WHO Multicenter Growth Reference Study (MGRS) [URL omitted from DDI.] released in 2006, which defined new standard anthropometry curves using a globally diverse reference population intended to reflect healthy growth conditions. For DHS samples that preceded WHO MGRS release, DHS retroactively calculated BMI-for-age Z scores using WHO MGRS reference data. DHS does not calculate BMI-for-age measures using the reference populations that preceded WHO MGRS (the 1978 U.S. CDC National Center for Health Statistics International Growth Reference data).

The original height and weight values used to calculate BMI are also included in the DHS. HWWEIGHT (HW2) reports the child's weight in kilograms as measured by DHS personnel; HWHEIGHT (HW3) reports the child's length or height in centimeters as measured by DHS personnel. See HWHEIGHT and HWHTHOWMEAS (HW15) for specifics on child length/height measurement. The related variable KIDAGEMO (HW1) reports the child's age in months at the time of measurement.