We clinicians constantly encounter patients with major depression in partial remission. They are no longer acutely depressed but continue to present with substantial functional impairment (Reference Paykel, Ramana and CooperPaykel et al, 1995). For treatment-resistant depression, only one pharmacological intervention can be recommended today with reasonable evidence, namely lithium augmentation (Reference Austin, Souza and GoodwinAustin et al, 1991; Reference Aronson, Offman and JoffeAronson et al, 1996), but this may not be the answer for those with low-grade residual depression.

Scott et al (Reference Scott, Teasdale and Paykel2000) demonstrated that cognitive therapy can help these people. Critically appraising their article in our evidence-based psychiatry case conference, however, it was very difficult for us to appreciate the substantive significance of this improvement, because only means and standard deviations of scores on the Social Adjustment Scale were reported. Analyses based on these data can show whether or not the treatment is better than the control condition, but cannot show how much better it is - a crucial piece of information for both patients and clinicians. We therefore resorted to the normative data for this scale (Reference Bothwell and WeissmanBothwell & Weissman, 1977). Calculation based on the means and standard deviations under the assumption of a normal distribution showed that, at week 20, 68% of patients with residual depression reached the 95% range of the control subjects when treated with clinical management plus cognitive therapy, whereas only 45% did so when treated with clinical management only. This translates into a ‘number needed to treat’ of 4.4 (95% CI 2.6-12.6).

This is an impressive figure. By adding 16 sessions of cognitive therapy to usual care, we can achieve social remission in one additional patient out of four, compared with continued standard care only. The original authors had concluded, “In patients showing only partial response to antidepressants, the addition of CT produced modest improvement in social and psychological functioning”. We find that the improvement was more than modest and would be clinically meaningful.