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Number of eligible children for height and weight/sampling procedure [message #8763] Mon, 14 December 2015 12:36 Go to next message
duke2015
Messages: 27
Registered: March 2015
Location: United States
Member
Hi there,

I am analyzing the 2011 Uganda DHS data using an outcome of child HAZ scores. I am trying to determine if I have merged the data correctly. I merged the household recode with the child recode data. My end result is 12, 293 records in total.

In the original household recode, there are 1654 children eligible for height and weight. I'm using Stata and got this number by: tab hv035. When I merge the household recode data with the child data, I get a total of 2705 children eligible for height and weight (tab hv035).

QUESTIONS:
1) Is it correct to have a total of 12,293 records after merging?
2) Why does the number of eligible children change when I merge the data sets?
2) Is it possible that some children are eligible for height and weight but don't have a measurement? Why would that happen?
3) How does the DHS determine in which households they will take anthropometric measurements?

Thank you, in advance!!
Re: Number of eligible children for height and weight/sampling procedure [message #8922 is a reply to message #8763] Thu, 14 January 2016 16:18 Go to previous messageGo to next message
Liz-DHS
Messages: 1393
Registered: February 2013
Senior Member
Dear User,
We are currently researching your query and will post as soon as we have a response.
As for reasons why H & W data may be missing for eligible children, there could be multiple reasons, such as interviewer error, or refusal.
Thank you!
Re: Number of eligible children for height and weight/sampling procedure [message #8931 is a reply to message #8763] Fri, 15 January 2016 11:15 Go to previous messageGo to next message
Liz-DHS
Messages: 1393
Registered: February 2013
Senior Member
Dear User,
Here is a response from one of our experts, Dr. Tom Pullum:
Quote:
Unfortunately, hv035 does not identify the eligibility of a specific child. I wish it did. Instead, it is the number of eligible children in the household and it is the same number for every record in the PR file (within the same household), regardless of age, etc. You can open the PR file and enter these lines:

keep if hvidx==1
tab hv035

You will see that there are 843 households with one eligible child, 653 with two, etc. The number of children will be 1*843 + 2*653 + ... = 2656. That, not 1654 or 2705, is the correct number of eligible children.

There is no need to do a merge. In the PR file the height-for-age variable is hc70. It is non-missing for 2636 children, although there are flagged and out-of-range values. The calculation of stunting would just use the hc70 values that are >-600 and <600. In the KR file the height-for-age variable is hw70. It is non-missing for 2214 children, including values that are flagged or out of range. Those 2214 children are the children in the household file whose mother is also in the household file and was interviewed. That is, if the mother has died or does not live in the same household as the child or was not interviewed, then the child who was in the PR file will not also be in the KR file.

DHS tables normally base the stunting (etc.) estimates on the children in the PR file, rather than the somewhat smaller number in the KR file. Children whose mother is not in the same household are generally a little worse off.

I suggest that you read about "_merge", a variable that is constructed whenever you do a merge. Normally you only want cases for which _merge===3, so you include a line "keep if _merge==3". Something else that I often do with complicated merges is to construct a variable that identifies the file. For example, after opening a PR file I will put "gen in_PR=1", and after opening a KR file I will have "gen in_KR=1". Then after the merge I could put "keep if in_PR==1 & in_KR==1", for example. If you do either of these things you should be able to discard the extra cases that are not in both files. I also do not use the new version of merge, with m:1, 1:m, etc., because it is too easy to get reversed and make a mistake.


Re: Number of eligible children for height and weight/sampling procedure [message #8948 is a reply to message #8931] Mon, 18 January 2016 11:06 Go to previous messageGo to next message
duke2015
Messages: 27
Registered: March 2015
Location: United States
Member
That is very helpful, thank you so much!

My follow-up question is this: how are households selected for anthropometry? Is the process standardized across DHS countries or would the process be Uganda-specific for the 2011 Uganda DHS?

It looks like all eligible children are measured within each selected household, however, not all households are selected for measurement. Is that correct?

Thank you!
Re: Number of eligible children for height and weight/sampling procedure [message #9006 is a reply to message #8948] Tue, 26 January 2016 15:50 Go to previous message
Liz-DHS
Messages: 1393
Registered: February 2013
Senior Member
Dear User,
Response from sampling expert, Dr. Ruilin Ren:
Quote:

The household selection for anthropometry across DHS surveys is quite standardized. In most of the cases, the households selected for anthropometry is a sub-sample consisting of one half or one third of the households selected for the women survey, depending on the sample size and fertility level. In a few countries with low fertility rate, or in some special cases for the purpose of a specific indicator related to children under five, anthropometry is conducted in all households selected for the women survey. In case of sub-sample selection of households for anthropometry, the selection procedure is systematic. In all cases, DHS never select children within household for anthropometry; it is always applied to all children under five found in the selected household. This is for survey efficiency considerations. All Uganda DHS surveys followed the standard procedure for anthropometry. Hope this is helpful.
Thanks
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