The placebo effect itself is an astonishing thing. In line with this, randomised trials that don’t use blinding tend to show larger treatment effects than blinded studies. Lack of blinding therefore means we risk over-estimating the effectiveness of a treatment.

In trials of psychological therapy, we’re unable to blind the patients and the therapists to whether they’re giving and receiving the ‘real’ treatment. With antidepressant medication however, it is possible to give some participants a placebo medication (sugar pill) and so they don’t know whether or not they are getting the real drug, which controls for the potentially inflating impact of expectations. The research group behind a recent meta-analysis (led by Pim Cuijpers) has published previous meta-analyses showing no significant difference between psychotherapy and medication for treatment of depression. Here, they ask whether the fact that medication can be blinded whereas psychotherapy can’t means that the effect of psychotherapy comparative to medication is over-estimated. Mental Elf Blog post.