# Subgroups in meta-analysis

I am reviewing a dissertation that does a meta-analysis of studies looking at a certain behaviour in rodents.

The author analysed ~20 studies and did a meta-analysis. They then split those studies into sub-categories, depending on the specific methodology that was used in each study (the same thing can be measured in several different ways) and performed one meta-analysis per group.

Finally, they split the original set in a different way (depending on another factor) and performed some further multiple meta-analyses.

I am really not that familiar with meta-analyses, so I am wondering whether this is good practice, or whether they should have included methodology as a factor in their overall analysis instead? If splitting data into multiple subgroups should there be a multiple comparison correction?

• just wondering. is this group in the algebra sense? or in the regular sense? seems regular but just double checking. (i saw this in hot network, and i remember i had this one statistics instructor who said something like - well it was in tagalog/filipino, so i'm not really sure - 'you know what i like about statistics? it has actual applications. unlike, say, group theory. oh wait. i think group theory has applications cryptography. hmm. (back to lesson)') – BCLC May 18 at 7:12
• @BCLC no, sorry, this is group in the "regular" sense... as "a subgroup of studies = a subset of the total studies". :) – nico May 18 at 7:41

The advantage of option (b) is that you have more data and hence your estimate of $$\tau^2$$ will be more precise. With 20 studies it was probably not very precise anyway (suggest they give confidence intervals for $$\tau^2$$ or $$I^2$$). A slight disadvantage of (b) is that it assumes that $$\tau^2$$ has the same value in each group but there are options in software to relax that assumption. There is detail on how to do this in R using the metafor package here.