Im currently working on a meta-analysis of randomized controlled trials, which examine the use of a certain graft in certain surgical intervention. In my pre-specified protocol, I planned to perform a subgroup analysis based on the thickness of the graft.
So the subgroup analysis was planned to be having two groups only:
Group A: Intervention with full-thickness graft
Group B: Intervention with thinned or half-thickness graft
However, I noted that there are 5 out of 17 studies that failed to provide if the graft was thinned or not.
My question is:
- Assume that the graft was not thinned and include them in Group A
- Simply remove these studies from the subgroup analysis
- Add a third subgroup labelled as "unknown thickness"
Which one makes the analysis properly conducted in this case?