Missouri has a treatment program considered key to battling drunken driving, but the state won't help the public understand which parts are effective and which aren't.

It's called the Substance Abuse Traffic Offenders Program, known by its acronym, SATOP.

Through a mix of incentives and court orders, most of those arrested for DWI go to one of 194 privately run centers to get screened and treated for any alcohol problems.

The centers are run by different organizations across the state. By law, they charge about $300 for each assessment, with a 10-hour treatment session costing $100.

Area prosecutors and judges point to the program as a key reason they feel comfortable granting plea deals that keep DWIs off most people's records.

But the state has never done a study to rank the effectiveness of each of those providers. At best, a 2008 study using 2004 numbers showed that, overall, nearly one in three people in the SATOP program were back for at least a second time.

The Post-Dispatch asked this year for the data to see how private providers fared at keeping first-time offenders from driving drunk again. To ensure confidentiality, the newspaper offered to take data without any information that identified individuals who got treatment.

The state refused to turn the numbers over.