All of these people had won substantial amounts of money before developing a compulsion to gamble.The meeting closed with the obligatory group prayer.
Toward the end of the meeting I was asked if I had any personal experience with gambling.
Without a doubt this had a significant effect on the demographics of the meeting.
Seven of the eleven (myself not included) members of that meeting were patients at the treatment center.
GA was the third major offshoot from Alcoholics Anonymous, preceded by Al-anon Family Groups, which was formally assembled in 1952, and Narcotics Anonymous founded in 1956. Each member introduces her or himself as a "compulsive gambler." The structure revolves around the 12 steps, the format allows each person to speak in turn, and discussion or "cross talk" is prohibited.
There is no formal study that I know of that has been conducted on the efficacy of GA.
As with any 12-step organization its reputation is founded on the testimonials of its satisfied members, which amounts to the catch phrase, "it works if you work it." There is no doubt that these groups do make some people very happy.