I am conducting a systematic review to compare the effect of intervention A vs. B on outcome Y (A, B, Y binary variables). So far the collected studies are categorized as below:
- 7 studies on both intervention A's effect on Y (A x Y) and B x Y
- 60 studies on A x Y
- 9 studies on B x Y
My questions are as follows:
In performing meta-analysis to compare A x Y and B x Y, is there any benefit (in terms of statistical strength of conclusion) to only pool the 7 studies that simultaneously study the effect of A & B on Y, in comparison to pooling 60 studies on A x Y and 9 studies on B x Y?
Of the 7 studies that simultaneously look at A x Y and B x Y, 4 studies found the effect of A x Y insignificant, but all found significant effect of B x Y. The effect sizes are similar. What are the risks of concluding that B has more significant effect on Y than A? I am aware of the risks associated with vote counting method, but in this case I am dealing with findings from identical set of studies.
I would very much appreciate any input or pointer to relevant literature/keywords. Thank you in advance.