Looks like you need to do your literature review. Why not use google scholar (or similar) to search on the key words Efficiency Merger and possibly also the industry you are looking at. Then from the key words or abstracts you should be able to identify the popular methodologies. you could also try terms such as productivity, profitability or even success instead of efficiency.
If you wanted to narrow your initial search you could start by looking for articles with "review" in them by adding this to your search terms. Then you can see if someone else has already done such a survey and you only need to update it.