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Trend Analysis using DHS data Sun, 17 May 2020 15:57
 sophyadam90 Messages: 2Registered: May 2020 Member
Hello,
I have grouped 3 Tanzania DHS datasets from TDHS 2004/05, TDHS 2010 and TDHS 2015/16. I want to analyze the trends of unmet need for modern contraception among sexually active adolescents across the 3 survey periods and check for linearity of trends. At first I only did a cross tabulation and obtained the proportions of trends in each survey year and by different background characteristics, later computed their changes over time. But this method did not seem proper in terms of actually checking for the significance of the trends of unmet need for modern contraception (where there was a significant change).
Re: Trend Analysis using DHS data [message #19277 is a reply to message #19260] Wed, 20 May 2020 09:01
 Bridgette-DHS Messages: 2021Registered: February 2013 Senior Member
Following is a response from DHS Research & Data Analysis Director, Tom Pullum:

This question is similar to another recent question about using the Nigeria 2008 and 2018 surveys for a difference-in-differences analysis. Please look at my response to that question regarding svyset. In your situation, you want to describe change in an outcome across three successive surveys. I suggest that you use v008 (century month of the interview) as a "time" variable, or construct "survey" to have the values 1, 2, 3 in the successive surveys. You would define Y=unmet need for modern contraception among sexually active adolescents. It would take the values 1, 0, or NA ("."). You test whether there was a difference between surveys 1 and 2 with a command such as "logit Y i.survey". (You would use svyset and svy and probably include covariates.) Under the default coding, survey 1 would be the reference category of "survey". The p-values for the coefficients for survey=2 and survey=3 would tell you whether the change from 1 to 2, or from 1 to 3, respectively, was significant. You would have to change the setup slightly to get at the significance of the change from 2 to 3. You could also get an annualized rate of change between surveys and 2 with "logit Y v008 if survey==1 | survey==2", and compare that with the annualized rate between 2 and 3. The significance of the coefficient for v008 would be almost exactly the same as the significance of the coefficient for survey 2 vs survey 1 in the other logit regression. Let us know if you have other questions.

Re: Trend Analysis using DHS data [message #19278 is a reply to message #19277] Wed, 20 May 2020 09:32
 sophyadam90 Messages: 2Registered: May 2020 Member
Thank you very much for the response. This was very useful.

Sophia
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