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?