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Home » Topics » Nutrition and Anthropometry » Input data for HAZ score calculation India DHS VI vs VII (Difficulty to understand z-score calculation input and replicating age data hw1)
Re: Input data for HAZ score calculation India DHS VI vs VII [message #25720 is a reply to message #25692] Wed, 30 November 2022 15:47 Go to previous message
Janet-DHS is currently offline  Janet-DHS
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Registered: April 2022
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Following is a response from DHS staff member Tom Pullum:

Age in days, b19, was not included in the KR and BR files before DHS-7. It is now included because day of birth is asked for all children, whereas it was previously asked only for children in the KR file (whether or not the survey included anthropometry).

Measurements of height and weight are included in the household survey, for all children, not just those who are in the KR file. Here are the names of the important dates in the PR file:

The child's birthdate (month, day, year): hc30, hc16, hc31;
Date of the household interview (month, day, year): hv006, hv016, hv007;
Date of the child's measurement (month, day, year): hc18, hc17, hc19.

The child's age in days on the day of interview is mdy(hv006, hv016, hv007) - mdy(hc30, hc16, hc31). However, the day of measurement is often the day after the day of interview, and occasionally later. The age in days on the day of measurement is mdy(hc18, hc17, hc19) - mdy(hc30, hc16, hc31).

The child's age in months on the day of the survey, hw1, is calculated as (mdy(hv006, hv016, hv007) - mdy(hc30, hc16, hc31))/30.4375, but it was previously calculated as v008-b3, where b3 is the cmc of the month of birth, hc30+12*(hc31-1900).

When day is missing, it is imputed as 16.

If you try to get the Z scores using the age in days on the day of measurement, you will probably do better but still will not get an exact match. When hc70-hc72 (the names of the Z scores in the PR file, hw70-hw72 in the KR file) are calculated during the construction of the standard recode files, I believe the height and/or weight measurements include an extra decimal place. What we see as height and weight in the PR file as hc3 and hc2 are not exactly the same as what was used to calculate the Z scores. I have never been able to get an exact match using the standard recode files. However, the differences are small, especially when aggregated with a mean, etc.

Hope I have not made any typos with the variable names above. Other forum users may want to add something. Also see the Guide to DHS Statistics ( x.cfm).
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