Although the effectiveness of psychotherapy is now widely recognised (e.g. American Psychological Association, 2013), questions about how much psychotherapy is necessary for client recovery remain. In response to these questions, two contemporary models of the association between the amount of treatment (number of sessions) and amount of change (in symptom distress) have emerged, each with supportive evidence. The first modelthe dose-effect (DE) model-was introduced by Howard and colleagues in the 1980s (Howard, Kopta, Krause, & Orlinsky, 1986). This model suggests that the likelihood of client recovery, when plotted with treatment duration, follows a negatively accelerated curve. That is, with each subsequent session, a greater proportion of clients will have recovered through treatment; however, the greatest gains in likelihood of recovery occur in the initial sessions and diminishing returns are seen as the session number increases. Based on this model, some have suggested that the early sessions of psychotherapy are more potent than later sessions (Baldwin,