A meta-analysis of 90 studies conducted in a variety of clinical, as opposed to laboratory, settings found psychotherapy in real-life situations to be effective (mean d = .41). Furthermore, increasing doses of psychological treatment lead to greater levels of positive outcomes.

The effects of psychological therapies under clinically representative conditions: A meta-analysis.

By Shadish, William R.; Navarro, Ana M.; Matt, Georg E.; Phillips, Glenn
Psychological Bulletin. 2000 Jul Vol 126(4) 512-529