Solved – Meta-analysis: splitting control group for multiple comparisons

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:

  1. Combine groups to create a single pair-wise comparison (recommended).
  2. Select one pair of interventions and exclude the others.
  3. Split the ‘shared’ group into two or more groups with smaller sample size, and include two or more (reasonably independent) comparisons.
  4. 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:

  1. a recent question on CrossValidated;
  2. a comprehensive website;
  3. the Cochrane toolkit;
  4. a recent book;
  5. 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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