Background Mental capacity is central to legal and ethical debates on the use of compulsion in psychiatry.

Aims To describe the clinical epidemiology of mental incapacity in patients with psychiatric disorders, including interrater reliability of assessments, frequency in the psychiatric population and associations of mental incapacity.

Method Cross-sectional studies of capacity to consent to treatment for psychiatric patients were systematically reviewed from Medline, EMBASE and PsycInfo databases. Information on the reliability of assessments, frequency and associations of mental incapacity was extracted.

Results Out of 37 papers reviewed, 29 different capacity assessment tools were identified. Studies were highly heterogeneous in their measurement and definitions of capacity. Interrater reliabilities between tools were high. Studies indicate incapacity is common (median 29%) but the majority of psychiatric in-patients are capable of making treatment decisions. Psychosis, severity of symptoms, involuntary admission and treatment refusal were the strongest risk factors for incapacity.

Conclusions Mental capacity can be reliably assessed. The majority of psychiatric in-patients have capacity, and socio-demographic variables do not have a major impact but clinical ones do.

Mental capacity is a multidimensional construct that is a central determinant of an individual’s ability to make autonomous decisions. Its assessment has become increasingly important with the move away from the paternalistic role of healthcare professionals towards a greater emphasis on an individual’s own treatment decisions (Schneider, 1998). The American Psychiatric Association has developed a model statute which uses a mental capacity test (Stromberg & Stone, 1983). In many other jurisdictions mental capacity and mental health legislation have developed along different lines to deal with the specific needs of different groups of patients. In both England and Scotland, mental capacity legislation has developed with the aim of providing a framework for people with either severe communication difficulties or cognitive problems (intellectual disability, dementia and other organic brain syndromes). In contrast, mental health legislation has developed with the needs of patients with psychiatric disorders – in particular, although not exclusively, psychotic disorders – in mind. Mental health legislation that does not use capacity tests generally applies a ‘status’ approach, whereby a wide range of treatments can be given to the patient on the basis of certain general conditions being met (e.g. the presence of a mental disorder, or the presence of perceived risk to the patient or others).

The use of status approaches has numerous implications. Under mental capacity legislation treatments are only provided in the patient’s best interests (with particular attention paid to previously expressed wishes, including advance directives, which have legal weight), whereas under mental health legislation best interests do not have to be considered, although in practice many psychiatrists effectively apply a best interests test (Peay, 2003). Further, the use of a ‘status’ approach means that the patient can be given a range of treatments, even if he or she might have capacity to refuse one or more of these. This has led some to suggest that current status-based approaches are anachronistic and unethical (Szmukler & Holloway, 1998) and that mental capacity and mental health legislation could be fused (Dawson & Szmukler, 2006).

A review of emergent case law literature in the USA (Grisso et al, 1997) has resulted in a ‘four abilities’ model, namely the ability to express a choice about treatment; the ability to understand information relevant to the treatment decision; the ability to appreciate the significance of that treatment information for one’s own situation; and the ability to reason with relevant information so as to engage in a logical process of weighing treatment options. Despite the influential work of the MacArthur Foundation (Grisso & Appelbaum, 1995a,b; Grisso et al, 1995), concern exists regarding the reliability of capacity assessments in individuals with a mental disorder, and the extent to which legislation that uses a capacity test covers the same or different groups of patients as mental health legislation which uses a status approach. Some have pointed to particular areas of perceived difficulty such as the area to appreciation, which may be difficult to operationalise (Saks et al, 2002; Breden & Vollmann, 2004).

Our aim was to make a systematic review of empirical, quantitative studies of mental capacity in order to answer the following three questions:

  1. Can the mental capacity of a patient be reliably assessed by two or more raters?
  2. What is the proportion of patients with psychiatric disorders in in-patient settings who are judged to lack capacity?
  3. What factors are associated with lack of capacity in individuals with psychiatric disorders?

Method
We aimed to identify all studies relevant to the aims of this review. Inclusion criteria were that the papers should be in the English language, describe defined populations of patients with psychiatric disorders; report quantitative research (i.e. research that produces numerical summaries of results, as opposed to qualitative research), and describe how the assessment of mental capacity was performed; capacity had to be assessed in relation to a current treatment decision, as opposed to capacity to make advance directives, capacity to participate in research, testamentary capacity or capacity to stand trial. Studies were excluded if they were conducted on children or young people less than 18 years old; exclusively concerned organic psychiatric disorders (dementia or delirium) or intellectual disability; were case reports, commentaries or review articles; or were retrospective case-note reviews.

Search strategy
Relevant research articles were identified from a systematic search of electronic data-bases. These comprised PsycInfo (1967 to July 2006), Medline (1996 to July 2006) and EMBASE (1980 to July 2006). The electronic database search terms were divided into three sets: mental health legislation terms (e.g. Mental Health Act, coercion, patients’ rights), disorder terms (e.g. schizophrenia) and capacity terms (e.g. incompetence, capacity, autonomy). The titles and abstracts of all articles generated were examined on the above inclusion and exclusion criteria. If the reviewer was uncertain as to whether an article fulfilled these criteria, the full paper was requested. The main reviewer was D.O. and his decision to include or exclude studies was reviewed for 100 abstracts by G.O. There were disagreements in 10 papers but further examination indicated none would have been eligible for the final review. The interrater reliability of reviewers was good ({kappa}=0.72). These searches were augmented by personal correspondence with experts on mental capacity research. Experts were identified from the investigators’ prior knowledge and a delegate list from a recent UK seminar which had advertised for researchers working on this area and included several international speakers. The International Journal of Law and Psychiatry was hand-searched from the first to the most recent issue. Finally, the bibliographies of retrieved articles were used to identify further articles.

Data analysis
Articles were categorised and data extracted corresponding to our three main questions. We extracted data from the full-length articles using forms to ensure the process was standardised. D.O. performed the data extraction but all studies were checked independently by M.H. As the papers were heterogeneous a formal meta-analysis was not attempted. Where possible we present median values and interquartile ranges. Where the data provided were sufficient to calculate a kappa value, we did so in order to provide a uniform measure of interrater reliability.

Full text

DAVID OKAI, BMedSci, MRCPsych
South London and Maudsley NHS Trust, and Academic Department of Psychological Medicine, Institute of Psychiatry, London

GARETH OWEN, BSc, MRCPsych
Academic Department of Psychological Medicine, Institute of Psychiatry, London

HUGH McGUIRE, MSc
Health Service and Public Health Research, Institute of Psychiatry, London

SWARAN SINGH, MD, FRCPsych, DM
Health Sciences Research Institute, University of Warwick

RACHEL CHURCHILL, MSc, PhD
Health Service and Public Health Research, Institute of Psychiatry, London

MATTHEW HOTOPF, MSc, PhD, MRCPsych
Academic Department of Psychological Medicine, Institute of Psychiatry, King’s College, London, UK

Correspondence: Professor Matthew Hotopf, Department of Psychological Medicine, Institute of Psychiatry, Weston Education Centre, 10 Cutcombe Road, London SE5 9RJ, UK. Tel: +44 (0) 20 7848 0778; fax: +44 (0) 20 7848 5408; email: .(JavaScript must be enabled to view this email address)