I think is a 90% because most people say they want to quit drinking, but when the time to quit comes they relapse during their first attempt. (or others may realize they can't quit so they decide to relapse on their first or second attempt)
This is something I found: Gloomy Addiction Relapse Statistics. Drug and alcohol rehab statistics show that the percentage of people who will relapse after a period recovery ranges from 50% to 90%.
*Hope it helps you*
Good luck!!~