[Alcoholic Anonymous] research tends to come to wildly divergent conclusions, often depending on an investigator’s biases. The group’s “cure rate” has been estimated at anywhere from 75 percent to 5 percent, extremes that seem far-fetched. Even the most widely cited (and carefully conducted) studies are often marred by obvious flaws. A 1999 meta-analysis of 21 existing studies, for example, concluded that AA members actually fared worse than drinkers who received no treatment at all. The authors acknowledged, however, that many of the subjects were coerced into attending AA by court order. Such forced attendees have little shot at benefiting from any sort of therapy—it’s widely agreed that a sincere desire to stop drinking is a mandatory prerequisite for getting sober.

Yet a growing body of evidence suggests that while AA is certainly no miracle cure, people who become deeply involved in the program usually do well over the long haul. In a 2006 study, for example, two Stanford psychiatrists chronicled the fates of 628 alcoholics they managed to track over a 16-year period. They concluded that subjects who attended AA meetings frequently were more likely to be sober than those who merely dabbled in the organization. … “I’ve been involved in a couple of meta-analyses of AA, which collapse the findings across many studies,” Tonigan says. “They generally all come to the same conclusion, which is that AA is beneficial for many but not all individuals, and that the benefit is modest but significant.” …

That statement is also supported by the results of a landmark study that examined how the steps perform when taught in clinical settings as opposed to church basements. Between 1989 and 1997, a multisite study called Project Match randomly assigned more than 1,700 alcoholics to one of three popular therapies used at professional treatment centers. The first was called 12-step facilitation, in which a licensed therapist guides patients through Bill Wilson’s method. The second was cognitive behavioral therapy, which trains alcoholics to identify the situations that spur them to drink, so they can avoid tempting circumstances. And the last was motivational enhancement therapy, a one-on-one interviewing process designed to sharpen a person’s reasons for getting sober. Project Match ultimately concluded that all three of these therapies were more or less equally effective at reducing alcohol intake among subjects. (more)

So apparently law makes alcoholics worse off by forcing them into AA.  And none of the above evidence shows AA is actually helpful to voluntary alcoholics.  More on Project Match.