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st: generalised estimating equations with unequally spaced data


From   NL Turner <Nicholas.Turner@bristol.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: generalised estimating equations with unequally spaced data
Date   Wed, 09 Jan 2013 12:04:01 +0000

Hi all,

I have a question about interpreting results from generalised estimating equations with unequally spaced data

My understanding is that normally with equally spaced time intervals e.g. on an annual basis, then a repeated exposure-outcome association can be modeled using in stata with the xtgee command to give an average effect over time e.g. the average effect of the exposure on outcome 1-year later. However, with a data set that I would like to use I have unequally spaced data, there is data at age 12-13 then 14-16 i.e. a 1-year interval for the first two measures and then a 2-year interval for the second two measures. I know that with certain correlation structures the xtgee command can cope with unequally spaced data but I'm not sure what the interpretation/time-frame of the output would be? Would the output be giving the average effect of the exposure on outcome 1.5-years later or something else?

Thanks
Nick


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