[R] using metafor for meta-analysis of before-after studies

[Michael Dewey]

At 18:39 04/04/2012, MP.Sylvestre at gmail.com wrote:
>Greetings,
>I wish to conduct a meta-analysis for which the outcome is a continuous
>variable measured on the same individuals before and after an intervention.
>Hence, the comparison is not made between two groups, but within groups, at
>diffrent times.
>
>Each study reports the mean outcome and SD before the intervention and the
>mean outcome and SD after the intervention. While p-values for paired
>t-test (or similar methods for paired data) are reported in the studies, no
>estimate of the variability of the individual differences are available.

If you know the p-value you can generate the t-value
If you know the t-value and the mean difference you can back 
calculate the standard errors of the differences.

Having said that I am not absolutely sure what the design of the 
primary studies you are analysing is so my answer may not apply 
directly to your problem.


>Can metafor deal with this sort of meta-analysis? I know that I can
>technically run metafor on these data, assuming that the groups are
>independent but my inference is likely to be wrong. On the other hand, I
>have no idea of the correlation within individuals.
>
>Thanks in advance,
>MP
>
>         [[alternative HTML version deleted]]

Michael Dewey
info at aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html