an overdose. An exit might involve expressing the anger in some way as an alternative to self-injuring behaviour. At the end of the therapy, patient and therapist each write "goodbye letters" which they exchange, summarising what has been achieved in the therapy and what remains to be done. After the end of the agreed number of weekly sessions, planned follow-up sessions take place to monitor and support the changes that have been made. Typically, a 16-session CAT might be followed up by a single session one month after the end of therapy, and a final one three months later. Evidence base CAT has been the subject of a number of research studies published in peer-reviewed journals. These include randomised controlled trials (RCTs) and other kinds of study. The approach is too new for any systematic reviews of RCTs to have been conducted, and therefore is not yet explicitly recommended by name by the UK National Institute for Health and Clinical Excellence (NICE). However NICE has recommended that there should be further research of CAT, for example in borderline personality disorder. A review of CAT research evidence published in 2014 reported that although there were five randomised controlled trials published, research evidence into the approach was dominated by small-scale, practice-based studies. These tended to be with complex and severe clinical groups; 44% of studies reviewed involved personality disorder. A review of CAT looking back over the 30 years to its beginnings contains a meta-analysis of 11 outcome studies of CAT. The overall number of patients treated in the studies was 324 and the average effect size across all studies was 0.83 (95% confidence interval 0.66–1.00). This is a large effect and suggests that CAT is efficacious in treating mental health problems. Evidence from randomised controlled trials CAT has been shown to lead to subjective improvement in people with anorexia nervosa. It has also been shown to produce significant improvements in adolescents with a diagnosis of borderline personality disorder. A different trial suggested that CAT for adult patients with personality disorders also showed improvements in symptoms and interpersonal functioning, as against controls who deteriorated on these measures. CAT has also been shown to improve patients' management of diabetes. An RCT of the use of a CAT-informed assessment for young people who had self-harmed suggested that it was effective in increasing rates of attendance at community follow-up. Evidence from other methodologies Comparative studies