P. Knekt, O. Lindfors, T. Härkänen, M. Välikoski, E. Virtala, M. A. Laaksonen, M. Marttunen, M. Kaipainen, C. Renlund, and the Helsinki Psychotherapy Study Group, in Psychological Medicine (2008, May), 38:689-703. doi:10.1017/S003329170700164X.
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