People with mental-health problems often express a preference about the kind of people they wish to be treated by and the kind of treatment they would prefer to receive. But there is some doubt about whether getting one's preferred treatment actually improves people's problems more than not getting their preferred treatment. Researchers in the U.S. reviewed 26 studies into this question involving more than 2,300 participants. They found that people matched to their preferred treatment had a 58% chance of showing a greater improvement than those who weren't matched, and were half as likely to drop out of treatment.
Swift, Joshua K. and Callahan, Jennifer L. - The impact of client treatment preferences on outcome: a meta-analysis Journal of Clinical Psychology April 2009, 65(4), 368-381