In a recent Round the Corner, Mitchell commented on a Cochrane Review of exercise therapy for chronic fatigue syndrome (CFS). One of the trials included in that review, and discussed by Mitchell, was the PACE trial. In this month's Round the Corner we are publishing a response we received from authors of the PACE trial (Chalder, White & Sharpe), together with Mitchell's reply. Ed.

Chronic fatigue syndrome (CFS) is syndrome of unremitting fatigue of at least 6 months' duration that causes significant disability. Exercise therapy has a proven track record in medicine and could be effective for some patients with CFS. An updated Cochrane review of eight studies appeared to suggest that exercise helps fatigue symptoms, but with only a small probability of recovery and/or improvement in daily function. Provisional data on acceptability suggest that most patients are willing to participate. However, one key study (PACE), which was well powered and influential in the Cochrane review, has been met with considerable controversy owing to lack of clarity on outcomes. Following release of the PACE study primary data, re-analysis suggested smaller effect sizes than initially reported.

Major depressive disorder in children and adolescents is common and associated with significant morbidity and mortality. This 2012 meta-analysis by Hetrick et al shows statistically significant, but small, improvements in depressive symptom scores and probability of remission with second-generation antidepressants (SGAs) compared with placebo. SGAs lead to a small, but significant, increase in risk of suicidal thoughts/attempts compared with placebo. Patients included in the primary studies had milder depression, less psychiatric comorbidity and less suicidality than those normally seen in clinical practice in the UK's National Health Service. However, primary studies had significant methodological shortcomings. Therefore, caution is needed when trying to generalise results to clinical practice.

Although a significant proportion of prisoners and patients in secure hospitals are sex offenders and victim surveys reveal a high level of hidden sexual victimisation, the authors of this Cochrane review found only very limited support for pharmacological intervention with sex offenders. Given the nature and extent of the problem of sexual offending and the promise shown by new drugs, there is a need for clinical scientists, lawyers and ethicists to rise to the challenge of ascertaining the effectiveness and safety of drugs which are being used to treat sex offenders, some involuntarily, without the evidence base to justify confidence as to their effectiveness and safety.

Psychotic depression is a severe condition. Drug treatment (antipsychotics, antidepressants or the combination) or electroconvulsive therapy (ECT) are both effective. However, a 2005 Cochrane review of drug treatments could not find a clear benefit for combination treatment with antidepressant and antipsychotic medication over antidepressants alone. The current updated Cochrane review (2015) incorporated two larger studies and found evidence of superiority for combination treatment. The review was constrained by the small number of available studies and could not address key questions such as the relative merits of antipsychotics and/or antidepressants compared with ECT or ketamine in acute treatment, and which treatments are best for long-term maintenance and prevention of recurrence. However, the methodology used was rigorous and the review gives the best summary to date of the evidence, as well as providing a platform for informing future research.

Parent–infant psychotherapy (PIP) is a psychoanalytic intervention that aims to improve parental and infant mental health. There is uncertainty about the clinical effectiveness of this intervention, particularly in comparison with other interventions. Based on a limited number of trials, this month's Cochrane Corner review aimed to summarise the best evidence available. Although the review found some tentative support for PIP in relation to attachment outcomes, overall the evidence was of low quality and PIP was not found to be more effective than treatment as usual or other interventions. This commentary contextualises and summarises the findings, and considers their implications for researchers and clinicians.

Revisions of international classification systems for mental disorders have focused on improving the reliability of diagnostic criteria. However, the uncertain validity of the current diagnostic categories means that they do not always fulfil their key purposes, namely to guide treatment and predict outcomes. This is especially true when traditional diagnostic approaches are applied to adolescents and young adults with emerging illnesses. A clinical staging model, similar to those used in general medicine, could improve diagnosis in psychiatry and aid treatment decision-making, especially if applied to individuals aged about 15–25 years, which is the peak age range for the onset of severe mental disorders. Staging models may offer a new framework for the development of interventions with high benefit and low risk, and for research into neurobiological and psychosocial risk factors. However, this approach is not without controversy: some experts oppose its introduction, some argue that it represents a transdiagnostic model, and some suggest it is only viable if disorder-specific models are used.

Modern legislation in the UK addressing the issue of decision-making ability uses tests of mental capacity based on the individual's ability to understand relevant information given to them. Alternative models of mental capacity do exist, but are largely considered defunct. This article reviews these alternative models and considers their importance. Far from being irrelevant to modern views on mental capacity, these models have already been incorporated into legislation such as the Mental Capacity Act 2005. A better understanding of these models can improve clinicians’ understanding of mental capacity in general. Modern controversies such as the impact of the United Nations Convention on the Rights of Persons with Disabilities (CRPD) are discussed and ways in which our understanding of mental capacity may have to change in the future are addressed.

Therapy for sexual problems is not solely based on findings from scientific studies; much of it has to do with intuitive knowledge that comes from personal and clinical experience. The author suggests that an ideal way to begin education about helping with patients' sexual identity, sexual function and relational concerns is to consider why sex is important. Answering this question illuminates the subtle roles sexual behaviour play in our lives. These roles are explained by providing clinically based responses to twelve questions: How are adults nurtured in sexual relationships? How is psychological intimacy created? What is learnt over time through sex? What accounts for the pleasures of sex? Why is sex important? Why is sexual experience unstable? What is a couple's sexual equilibrium? What is sensuality? Is a life of sexual pleasure possible? What is sexual health? What are the sources of distress about sex? How do these concepts facilitate therapy?