What’s right with it?!
Most of us take a qualitative approach to reviewing the literature for no reason other than that’s what we were taught to do or what we’ve read. But there are at least four problems with narrative reviews:
- they are rarely comprehensive
- they are highly susceptible to reviewer bias
- they seldom take into account differences in the quality of studies
- they often come to the wrong conclusion or no conclusion at all, hence the oft-heard call for further research
On each count meta-analysis offers a superior alternative.
For more, see The Essential Guide to Effect Sizes.