Randomised controlled trials and systematic reviews are all very well, but in medical practice we are often trying to modify ingrained patient behaviours over a series of encounters, and you might think that is an impossibly complex process to analyse and measure. Well, it certainly is possible to do randomised trials of specific techniques and come up with measurable endpoints: motivational interviewing is a technique developed for helping to change lifestyle, and a meta-analysis of studies (

) shows that it can lower measures of blood alcohol, cholesterol, body mass index, and blood pressure. Some trials also show that it can be done in 15 minute sessions, and not necessarily by a doctor. A meta-analysis of psychotherapy for post-traumatic stress disorder (PTSD) in

is less easy to interpret: the comparator was not an untreated group but a group receiving the same type of treatment for another condition, or a different kind of psychological treatment for …