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Duffy et al provide evidence for the effectiveness of cognitive therapy in post-traumatic stress disorder (PTSD) in the context of terrorism and civil conflict in Northern Ireland.¹ More information would have been helpful to interpret the results.

No patients were started on medications during the trial. However, 52% in the immediate therapy group were taking antidepressants already. When were these initiated in relation to the trial? Also, were any changes to the antidepressant dose allowed during the trial? Over 70% in the immediate therapy group had comorbid major depression. The effect of antidepressant initiation just before the trial or dose changes may be partly responsible for the improvement in this group's symptoms.

The percentages for the overall effectiveness of cognitive therapy are the combined scores of the immediate treatment and waiting list control groups. This makes them uncontrolled scores. The authors are not comparing two groups of patients, one receiving therapy and the other not receiving therapy.

The follow-up mean scores in table 3 have been taken at either four or 12 months. As a clinician, I would be particularly interested in information about the maintenance of gains at 12 months. This is not clear from the table. If gains seen at four months are lost by 12 months, this then raises questions about whether booster sessions are indicated.

Finally, the therapist effect is important. It would be interesting to look at whether this difference in patient scores is related to the type of qualification in cognitive therapy that the therapists had. Recent research has shown that formal post-qualification training in cognitive therapy is associated with competence.²