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Re: st: Meta-analysis and corr2data


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Meta-analysis and corr2data
Date   Tue, 09 Mar 2004 08:41:54 -0500

At 01:48 AM 3/9/2004 -0800, n p wrote:

statistics etc.). The question is if it is right to
use the corr2data command to create three (or more)
independent samples for A, B and C arms with given
mean, SE and N to obtain via regression two betas and
two SEs (B vs. A and C vs. A). I know that I could use
only two arms for each meta-analysis ( B vs. A, C vs.
A and so on) but I think that this would induce some
multiple comparison error so I decided that I have to
calculate all possible betas of each study ( B vs. A,
C vs. A and so on) simultaneously.
I think you could. You would run corr2data multiple times to create each of the fake data sets, adding an indicator to each data set to indicate which group it was (e.g. gen group = 1, gen group = 2, etc.) Then, combine all the files together.

If in doubt as to whether what you are doing with corr2data is legit: Generate alternative data sets, using a different seed. Results should be exactly identical, down to several decimal places. If not, what you are doing is probably illegitimate. For example, computing logs of variables would not be legitimate.

Basically, the idea behind corr2data is that you can use it when the means, correlations and standard deviations are sufficient to do all the required calculations. If anything more than that is needed, corr2data can't handle it. In some programs, like SPSS, you could enter means, correlations and SDs directly. In Stata, you achieve the same thing via the creation of fake data with the desired means, etc. But, you have to remember that the data are fake! And what you can do is limited.

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Richard Williams, Notre Dame Dept of Sociology
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