To date, few studies have been published on the dose-response relationship, but there is general consensus that between 13 and 18 sessions of therapy are required for 50% of patients to improve. Reviewing the clinical trials literature reveals that in carefully controlled and implemented treatments, between 57.6% and 67.2% of patients improve within an average of 12.7 sessions. Using naturalistic data, however, revealed that the average number of sessions received in a national database of over 6,000 patients was less than five. The rate of improvement in this sample was only about 20%. These results suggest that patients, on average, do not get adequate exposure to psychotherapy, nor do they recover from illness at rates observed in clinical trials research.