Has anyone done a study of support groups?

I find this an interesting phenomenon and one that has not gotten the recognition that it deserves. I suppose that in an informal sense support groups have always been around, but I am talking about the ones that gives themselves names and seek outsiders. I don’t know if AA is the first such group but I would think that it is among the first and certainly the best known. Although AA is international, I believe that support groups have caught on mostly in the U.S. Part of the reason for the lack of recognition is that most support groups exist for the mutual benefit of their members and do not seek outside recognition. Usually the members have not had any training, but share some particular problem.

It would be interesting to learn some more about support groups. How many are there? How many members do they have? How long do they tend to last? How successful are they? What characteristics do successful ones have? Which are the ones that have grown to the extent that they have multiple chapters?