Their personal testimonies which have been witnessed by millions and millions. And those making the testimonies don't have to cite anything either because they are talking about their own first hand experience. And it really doesn't matter what the success "rate" is, if you've got an alternative that has produced millions and millions of firsthand advocates over a period of decades I'd be happy to hear it out. If you know of a "different method that may have helped them" they lets hear about it.
All hearsay.
Of the people witnessed to be claiming to be helped by AA, how many were telling the truth? And many more AA members might have been quit drinking outside of AA?
For all we know, AA could be holding more people back from sobriety than it is helping.