I am conducting a meta-analysis in which some of the studies compare two or more interventions to the same control. The Cochrane Handbook recommends:
- Combine groups to create a single pair-wise comparison (recommended).
- Select one pair of interventions and exclude the others.
- Split the ‘shared’ group into two or more groups with smaller sample size, and include two or more (reasonably independent) comparisons.
- Include two or more correlated comparisons and account for the correlation.
The third option is the only feasible one. How do I calculate the mean and SD of the split control group?
Definitely you need to go beyond the traditional paradigm of pairwise meta-analysis, and instead conduct a network meta-analysis (in this case an adjusted indirect comparison given the star-shaped evidence network).
You can find ample references on this, such as:
- a recent question on CrossValidated;
- a comprehensive website;
- the Cochrane toolkit;
- a recent book;
- an upcoming book.
You can easily do network meta-analysis with R, Stata, or WinBUGS. I recommend you to use R, for instance the netmeta package.
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