Hi, I'd appreciate some help on the following:
A systematic review looks to compare the effectiveness of two interventions, A and B, in a particular population, X.
The interventions, though, are commonly used in a discrete population Y also.
Some of the studies retrieved compare A and B just in the desired population X, but others compare the interventions in a mix of populations X and Y.
In the latter there may not have been block randomisation so the proportions of X and Y receiving A or B may be unbalanced.
In doing a meta-analysis of these studies, should one be cautious in looking to combine the results from the X-only studies with those extracted from the X-Y mixed studies? Does it matter that in removing the subgroup X from the mixed study the original randomisation has been disrupted and does it matter that the A and B intervention groups may be then be unbalanced?
Would it be reasonable to test for the significance of this with sensitivity analysis by removing the results from the mixed studies after the meta-analysis?