Studies on relations between number of sessions and effect of psychotherapy have usually assumed a constant rate of change across different lengths of therapy, explained by a model called the dose-effect model. This assumption has been challenged by the good-enough level (GEL) model, which makes the prediction that the rate of change will vary as a function of total number of sessions. This study aimed to compare these models. We also assessed the relationship between reliable and clinically significant change (RCSI) and total dose of therapy. Participants were drawn from two datasets in the Swedish primary care (n = 640) and adult psychiatric care (n = 249). The participants made session-wise ratings on the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM). Multilevel analyses indicated a better fit using the GEL-model, with some reservations concerning RCSI and patterns of change. The results may indicate a general lawful relationship that may have implications for future research, as well as psychotherapy practice and policy making.

This study examines psychotherapy response in connection to treatment duration and maintenance of treatment gains. The dose-effect perspective (Howard et al. 1986) first proposed applying medical terminology to investigate a level of exposure to a dose of psychotherapy (in number of sessions) where individuals can expect to receive sufficient benefit (i.e., 48 -- 58% of clients can be expected to sufficiently benefit from therapy by 8 sessions). The proponents of the Good Enough Level (Barkham et at. 2006) argued that mere exposure to therapy is not an effective measure for client benefit, but rather that client responses to therapy vary. They contend that instead of recommendations for attending a certain number of sessions (dose-effect) that individuals who attend psychotherapy will discontinue attending therapy when they have obtained sufficient benefit (good enough level). Archival data of university students who previously attended individual therapy were obtained and subjects were contacted via email to take a survey and follow up measure of general well being. Those individuals who completed the Outcome Questionnaire-45 were selected for the study and their treatment response was analyzed in connection to treatment duration measured in number of sessions attended. 288 met criteria for the current study, consisting of 197 women and 91 men ranging in age from 17 to 52 (M= 21). Conclusions obtained from this study indicate that treatment duration is not a factor in subjects having positive outcomes to psychotherapy. Additionally, there was not a significant difference among subjects who were able to maintain treatment gains and the number of session attended in treatment. These results offer support for the Good Enough Level model of treatment response suggesting that individuals respond to therapy differently and discontinue when they have received sufficient benefit. Implications for these findings are discussed along with limitations of the current study.