R help - Apr 2012 - using metafor for meta-analysis of before-after studies

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.

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

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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