A survival analysis of clinically significant change in outpatient psychotherapy

The number of sessions required to produce meaningful change has not been assessed adequately, in spite of its relevance to current clinical practice. Seventy-five clients attending outpatient therapy at a university-affiliated clinic were tracked on a weekly basis using the Outcome Questionnaire (Lambert et al., 1996) in order to determine the number of sessions required to attain clinically significant change (CS). Survival analysis indicated that the median time required to attain CS was 11 sessions. When current data were combined with those from an earlier investigation (Kadera, Lambert, and Andrews, 1996), it was found that clients with higher levels of distress took 8 more sessions to reach a 50% CS recovery level than clients entering with lower levels of distress. At a six-month follow-up, CS gains appeared to have been maintained. Other indices of change also were examined (reliable change, average change per session). The implications of these results for allocating mental-health benefits, such as the number of sessions provided through insurance, are discussed.