Decisional capacity is a term that has its origins in legislation, but has considerable implications for clinical practice. Definitions vary but research in this area has centred on a model published by Paul Appelbaum and Thomas Grisso in 1995, who conceptualised capacity in terms of four abilities: ability to communicate a choice, ability to understand relevant information, ability to appreciate relevant information and ability to manipulate information rationally. ^{Reference Appelbaum and Grisso1} In healthcare, treatment decision-making capacity – hereinafter referred to as ‘capacity’ – is closely related to agency (the capacity of a person, or ‘agent’, to take intentional action), autonomy and the exercise of self-governance, concepts that are fundamental to human dignity and rights. ^{Reference Owen, Freyenhagen, Richardson and Hotopf2} For example, Article 12 of the United Nations Convention on the Rights of Persons with Disabilities recognises the right to be recognised as a person before the law, and the subsequent right to have one's decisions legally recognised. Autonomy and empowerment are thought to be essential components of patient-defined recovery from psychosis, ^{Reference Pitt, Kilbride, Nothard, Welford and Morrison3,Reference Law and Morrison4} and mental health legislation frequently requires clinicians to empower patients to make decisions and to make an assumption of capacity until proved otherwise, e.g. the Adults with Incapacity (Scotland) Act (2000) and the Mental Capacity Act 2005. However, there is also a concern that if patients who lack capacity to make specific decisions are allowed to make these decisions, then these may not reflect their true wishes, with the consequence being a poor outcome and inadequate protection of the patient. ^{Reference Lepping and Raveesh5} Capacity has understandably been called the ‘gatekeeper for autonomy’. ^{Reference Donnelly6} Lepping et al found that the average percentage of patients with impaired capacity on psychiatric wards is 45%. ^{Reference Lepping, Stanly and Turner7} Despite the frequency with which psychiatrists are asked to make such judgements, almost half of them view the evidence base in this area as weak. ^{Reference Hamann, Cohen, Leucht, Busch and Kissling9} Nonetheless, the field of decision-making capacity research has grown in recent years. This has been spurred on by changes in legislation, but also by a change in the culture in which healthcare decisions are made. People using mental health services are showing a greater desire to be included in decisions about their treatment, ^{Reference Hamann, Cohen, Leucht, Busch and Kissling9} and there has been an increasing emphasis on ensuring not only that patients give informed consent to treatment, but also that they are actively involved in the decision-making process. ¹⁰ The most common model for such involvement is called ‘shared decision-making’, but there is evidence that people with psychosis do not typically experience this. ¹¹ Since impaired capacity is a major barrier to psychiatrists implementing shared decision-making with people with psychosis, ^{Reference Hamann, Mendel, Cohen, Heres, Ziegler and Buhner12} improving our understanding of factors that cause or maintain this impairment may help to change this. Moreover, British Medical Association guidance on assessing and managing capacity advises that it is the duty of the assessing clinician to enhance capacity where it is possible to do so. ¹³ In the context of psychiatric and mental health conditions, this is often achieved through treatment of the condition itself; however, there has been little research on the effectiveness of current treatments for enhancing decision-making capacity. Although some studies have examined whether specific psychological and educational interventions can enhance capacity, ^{Reference Carpenter, Gold, Lahti, Queern, Conley and Bartko14,Reference Naughton, Nulty, Abidin, Davoren, O'Dwyer and Kennedy15} the overall evidence is surprisingly limited.

Previous reviews have examined the prevalence of incapacity in psychiatric patients, ^{Reference Okai, Owen, McGuire, Singh, Churchill and Hotopf16} the reliability and validity of measurement tools, ^{Reference Dunn17,Reference Sturman18} the degree of impairment in decisional capacity in schizophrenia, ^{Reference Jeste, Depp and Palmer19} the role of poor insight, ^{Reference Ruissen, Widdershoven, Meynen, Abma and van Balkom20} and the role of specific neuropsychological deficits. ^{Reference Palmer and Savla21} Although one older review examined the correlates of capacity in psychiatric populations generally, ^{Reference Okai, Owen, McGuire, Singh, Churchill and Hotopf16} no review has yet looked at the factors associated with capacity in psychosis specifically. Identifying these factors might help us develop a clinically useful theoretical model, which in turn would aid the development of effective interventions to support capacity. Thus, the primary objectives of this systematic review were to identify which clinical, demographic and treatment-related variables are associated with treatment decision-making capacity in psychosis and, where a sufficient number of comparable studies exist, to use meta-analysis to produce pooled estimates of the magnitude and reliability of any relationship.

Results

Of the 2057 papers initially identified, 1994 were excluded after inspection of title or abstract (Fig. 1). Full-text publications were sought for the remaining 63 papers. Of these, 40 were excluded: 21 did not include a measure of capacity or did not examine or report correlates, 12 were case descriptions, editorials or reviews, 4 examined a different population and 2 examined research decision-making capacity. A full list of excluded studies with reasons for exclusion is provided in online supplement DS3. A total of 23 studies were included for review (Table 1). These provided data on the relationship between capacity and symptoms (fc = 12), insight (k = 4), affect (k = 3), cognitive performance (k = 6), executive functioning (k = 2), duration of illness (k = 2), education (k = 5), metacognition (k = 1) and various interventions (k = 10). ‘Metacognition’ refers to the implicit and explicit awareness, knowledge, beliefs and understanding we have about our cognitive systems and processes.

Fig. 1 Study selection.

Table 1 Characteristics of included studies

	Participants					Baseline demographics
Study	Total n	Proportion with psychosis, %	Country	Measure of capacity	Variables measured (name of measure)	Age, years: mean (s.d. or range)	Proportion female, %	Treatment setting
Cairns et al (2005) Reference Cairns, Maddock, Buchanan, David, Hayward and Richardson35	112	55	England	MacCAT-T	Psychotic symptoms (BPRS) Insight (SAI-E) Cognition (MMSE) Coercion (BPCS)	37.2 (11.8)	37	In-patient
Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36	60	100	France	MacCAT-T	Psychotic symptoms (PANSS) Insight (SUMD) Depression (BDI-2) Anxiety (STAI)	36.3 (10.9)	28	Out-patient
Di & Chen (2013) Reference Di and Cheng70	192	100	China	SSICA	Psychotic symptoms (BPRS) Years of education	30.3 (15.2)	19	In-patient
Dornan et al (2015) Reference Dornan, Kennedy, Garland, Rutledge and Kennedy48	37	89	Ireland	MacCAT-T	Psychotic symptoms (PANSS) Functioning (GAF)	32.3 (19.8–56.4)	8	In-patient (forensic)
Elbogen et al (2007) Reference Elbogen, Swanson, Appelbaum, Swartz, Ferron and Van Dorn38	469	59	USA	DCAT-PAD	Psychotic symptoms (BPRS) Functioning (GAF) Insight (ITAQ) Cognition (AMNART; WAlS-III; COWAT; HVLT)	42 (10.7)	60	Out-patient
Grisso & Applebaum   (1991) Reference Grisso and Appelbaum71	26	100	USA	MUD	Psychotic symptoms (BPRS) Depression (BDI) Cognition (WAIS-R)	36.8 (NS)	31	In-patient
Grisso & Applebaum   (1995) Reference Grisso and Appelbaum72	75	100	USA	UTD, POD, TRAT	Psychotic symptoms (BPRS) Depression (BDI) Cognition (WAIS-R)	35.4 (7.4)	48	In-patient
Grisso et al (1997) Reference Grisso, Appelbaum and Hill-Fotouhi31	40	100	USA	MacCAT-T	Psychotic symptoms (BPRS)	39 (NS)	20	In-patient
Hamann et al (2011) Reference Hamann, Mendel, Meier, Asani, Pausch and Leucht49	61	100	Germany	Clinical	Controlled trial; no correlationa data reported	40.7 (11.7)	62	In-patient
Howe et al (2005) Reference Howe, Foister, Jenkins, Stene, Copolov and Neks73	110	81	Australia	MacCAT-T	Psychotic symptoms (PANSS)	37.2 (12.3)	51	In-patient
Kennedy et al (2009) Reference Kennedy, Dornan, Rutledge, O'Neill and Kennedy45	88	74	Ireland	MaCAT-T	Uncontrolled trial; no other correlational data reported	NS	9	In-patient (forensic)
Koren et al (2005) Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33	21	100	Israel	MacCAT-T	Metacognition (WCST) Cognition (WAIS-R)	23.9 (4.5)	38	In-patient
Kleinman et al (1996) Reference Kleinman, Schachter, Jeffries and Goldhamer44	26	100	Canada	Knowledge of medication	Controlled trial; no correlationa data reported	NS	NS	In-patient
Mandarelli et al (2012) Reference Mandarelli, Parmigiani, Tarsitani, Frati, Biondi and Ferracuti34	45	56	France	MacCAT-T	Psychotic symptoms (BPRS) Cognition (WCST) Cognition (MMSE)	41 (13.1)	55	In-patient
Munetz & Roth (1985) Reference Munetz and Roth42	25	88	USA	Questionnaire	Uncontrolled trial; no other correlational data reported	48.6 (NS)	66	NS
Naughton et al (2012) Reference Naughton, Nulty, Abidin, Davoren, O'Dwyer and Kennedy15	19	95	Ireland	MacCAT-T	Uncontrolled trial; no other correlational data reported	36.7 (10.6)	100	In-patient (forensic)
Owen et al (2008) Reference Owen, Richardson, David, Szmukler, Hayward and Hotopf74	40	100	England	MacCAT-T	Psychotic symptoms (BPRS) Cognition (WAIS-R) Insight (SAI-E)	NS	NS	In-patient
Palmer et al (2002) Reference Palmer, Nayak, Dunn, Appelbaum and Jeste43	16	94	USA	MacCAT-T; HCAT	Psychotic symptoms (PANSS, BPRS) Cognition (DRS)	54.6 (7.2)	44	Out-patient
Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39	60	100	France	MacCAT-T	Psychotic symptoms (PANSS) Insight (BCIS) Depression (BDI-2) Anxiety (STAI)	36.8 (11.1)	32	Out-patient
Rutledge et al (2008) Reference Rutledge, Kennedy, O'Neill and Kennedy32	102	88	Ireland	MacCAT-T	Psychotic symptoms (PANSS) Functioning (GAF)	38.1 (16.2)	9	In-patient (forensic)
Schacter et al (1994) Reference Schacter, Kleinman, Prendergast, Remington and Schertzer75	59	100	Canada	Questionnaire	Psychotic symptoms (BPRS)	37 (NS)	17	Out-patient
Wong et al (2000) Reference Wong, Clare, Holland, Watson and Gunn46	19	100	England	Interview	Psychotic symptoms (BPRS)	40.1 (10.6)	24	Out-patient
Wong et al (2005) Reference Wong, Cheung and Chen40	81	100	Hong Kong	MacCAT-T	Psychotic symptoms (PANSS) Depression (MADRS) Insight (DAI) Cognition (WAIS-R-HK; WCST; WMS; MCT)	36.9 (10.4)	46	In-patient

AMNART, American National Reading Test; BCIS, Beck Cognitive Insight Scale; BDI, Beck Depression Inventory; BDI-2, Beck Depression Inventory – 2nd edn; BPCS, Brief Perceived Coercion Scale; BPRS, Brief Psychiatric Rating Scale; COWAT, Controlled Oral Word Association Test; DAI, Drug Attitude Inventory; DCAT-PAD, Decisional Competence Assessment Tool for Psychiatric Advance Directives; DRS, Mattis Dementia Rating Scale; GAF, Global Assessment of Functioning; HCAT, Hopkins Competency Assessment Test; HVLT, Hopkins Verbal Learning Test; ITAQ, Insight and Treatment Attitudes Questionnaire; MacCAT-T, MacArthur Competence Assessment Tool-Treatment; MADRS, Montgomery & Asberg Depression Rating Scale; MCT, Monotone Counting Test; MMSE, Mini Mental State Examination; MUD, Measuring Understanding of Disclosure; NS, not stated; PANSS, Positive And Negative Syndrome Scale; POD, perceptions of Disorder; SAI-E, Expanded Schedule for the Assessment of Insight; SSICA, Semi-structured Inventory for Competence Assessment; STAI, Spielberger State Trait Anxiety Inventory; SUMD, Scale to Assess Unawareness of Mental Disorder; TRAT, Thinking Rationally about Treatment; UTD, Understanding Treatment Disclosure; WAIS-III, Wechsler Adult Intelligence Scale – 3rd edn; WAIS-R, Wechsler Adult Intelligence Scale-Revised; WCST, Wisconsin Card Sorting Test; WAIS-R-HK, Wechsler Adult Intelligence Scale – Revised – Hong Kong; WCST, Wisconsin Card Sorting Task; WMS, Wechsler Memory Scale.

Quality assessment

Overall GRADE ratings for each outcome are presented in the right-hand columns of Tables 2, 3 and 4. Quality ratings using the AHRQ measure of observational and uncontrolled intervention studies are shown in online Tables DS1 and DS2, and online Table DS3 provides Cochrane risk of bias ratings for randomised controlled trials. The studies generally performed well on the AHRQ and Cochrane risk of bias assessments. Methods used to assess key outcomes were generally reliable and valid, cohorts were as a rule well described and characterised, and most of the studies selected their participants in a relatively unbiased way (although convenience samples were widely used). The evidence was weakened by a general failure to provide prespecified power calculations. Although only a minority of studies (k = 5) had masked rater assessment of the relevant outcomes, we made a post hoc decision to exclude this from the quality assessment. Intervention studies often did not include a follow-up assessment. Funnel plots did not detect evidence of publication bias for the majority of the outcomes, but there were generally too few studies to assess this properly. ^{Reference Ioannidis and Trikalinos30}

Table 2 Summary of meta-analytical estimates

Outcome (number of studies)	Included studies	n	Pooled Fisher's Z (95% CI) Pooled r (95% CI)	Heterogeneity (I 2 for Z), %	Quality (GRADE)
Relationship between total symptom severity and understanding (9 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Grisso & Applebaum (1991) Reference Grisso and Appelbaum71 Grisso & Applebaum (1995) Reference Grisso and Appelbaum72 Grisso et al (1997) Reference Grisso, Appelbaum and Hill-Fotouhi31 Howe et al (2005) Reference Howe, Foister, Jenkins, Stene, Copolov and Neks73 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Rutledge et al (2008) Reference Rutledge, Kennedy, O'Neill and Kennedy32 Schacter et al (1994) Reference Schacter, Kleinman, Prendergast, Remington and Schertzer75 Wong et al (2005) Reference Wong, Cheung and Chen40	610	Z = −0.49 (−0.62 to −0.35) r = −0.45 (−0.55 to −0.33)	60	Moderate (−1 risk of bias)
Relationship between total symptom severity and appreciation (6 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Grisso et al (1997) Reference Grisso, Appelbaum and Hill-Fotouhi31 Howe etal (2005) Reference Howe, Foister, Jenkins, Stene, Copolov and Neks73 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Rutledge et al (2008) Reference Rutledge, Kennedy, O'Neill and Kennedy32 Wong et al (2005) Reference Wong, Cheung and Chen40	453	Z = −0.24 (−0.33 to −0.14) r = −0.23 (−0.14 to −0.32)	0	Moderate (−1 risk of bias)
Relationship between total symptom severity and reasoning (7 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Grisso & Applebaum (1995) Reference Grisso and Appelbaum72 Grisso et al (1997) Reference Grisso, Appelbaum and Hill-Fotouhi31 Howe et al (2005) Reference Howe, Foister, Jenkins, Stene, Copolov and Neks73 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Rutledge et al (2008) Reference Rutledge, Kennedy, O'Neill and Kennedy32 Wong et al (2005) Reference Wong, Cheung and Chen40	528	Z = −0.32 (−0.52 to −0.12) r = −0.31 (−0.48 to −0.12)	80	LOW (−1 risk of bias, −1 inconsistency)
Relationship between depression and understanding (3 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Grisso & Applebaum (1991) Reference Grisso and Appelbaum71 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39	146	Z = −0.04 (−0.21 to 0.13) r = −0.04 (−0.20 to 0.13)	0	Moderate (−1 imprecision)
Relationship between verbal IQ and understanding (4 studies)	Grisso & Applebaum (1991) Reference Grisso and Appelbaum71 Grisso & Applebaum (1995) Reference Grisso and Appelbaum72 Koren et al (2005) Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33 Wong et al (2005) Reference Wong, Cheung and Chen40	203	Z = 0.45 (0.20 to 0.69) r = 0.42 (0.20 to 0.60)	60	Low (−1 risk of bias, −1 imprecision)
Relationship between verbal IQ and reasoning (3 studies)	Grisso & Applebaum (1995) Reference Grisso and Appelbaum72 Koren et al (2005) Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33 Wong et al (2005) Reference Wong, Cheung and Chen40	177	Z = 0.42 (0.27 to 0.57) r = 0.39 (0.26 to 0.51)	0	Low (−1 risk of bias, −1 imprecision)
Relationship between years of education and understanding (3 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Wong et al (2005) Reference Wong, Cheung and Chen40	201	Z = 0.49 (0.35 to 0.63) r = 0.46 (0.34 to 0.56)	0	Moderate (−1 imprecision)
Relationship between years of education and reasoning (3 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Wong et al (2005) Reference Wong, Cheung and Chen40	201	Z = 0.26 (0.12 to 0.40) r = 0.26 (0.12 to 0.38)	0	Moderate (−1 imprecision)

Table 3 Summary of individual observational study findings

Correlate (number of studies)	Studies included	n	Outcome measures used	Key findings	Quality (GRADE)
Executive functioning (2 studies)	Koren et al (2005) Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33 Mandarelli et al (2012) Reference Mandarelli, Parmigiani, Tarsitani, Frati, Biondi and Ferracuti34	66	WCST	Some evidence of large correlations in one study, but no clear evidence in the other	Very low (−1 risk of bias, −1 inconsistency, −1 imprecision)
Insight (5 studies)	Cairns et al (2005) Reference Cairns, Maddock, Buchanan, David, Hayward and Richardson35 Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Owen et al (2009) Reference Owen, David, Richardson, Szmukler, Hayward and Hotopf37 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Elbogen et al (2007) Reference Elbogen, Swanson, Appelbaum, Swartz, Ferron and Van Dorn38	813	SUMD, SAI-E, BCIS, ITAQ	Insight strongly and significantly associated with capacity, and reasoning in particular	Moderate (−1 risk of bias, −1 indirectness, +1 large effects)
Duration of illness (2 studies)	Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39 Wong et al (2005) Reference Wong, Cheung and Chen40	141	Years since diagnosis	Some evidence of small correlation in one study, but no clear evidence in the other	Low (−1 risk of bias, −1 imprecision)
Metacognitive ability (1 study)	Koren et al (2005) Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33	21	Participant ratings of confidence in the correctness of the sort (0–100)	Metacognitive ability found to be associated with capacity	Moderate (−2 imprecision, +1 large effect)
Perceived coercion (1 study)	Cairns et al (2005) Reference Cairns, Maddock, Buchanan, David, Hayward and Richardson35	112	BPCS	Participants judged to have impaired capacity were more likely to report high perceived coercion	Moderate (−1 imprecision)
Anxiety (2 studies)	Capdevielle et al (2009) Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36 Raffard et al (2013) Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39	120	STAI	Both state and trait anxiety had small to medium positive correlations with appreciation and reasoning, but not with understanding or communicating	Moderate (−1 imprecision)

BCIS, Beck Cognitive Insight Scale; BPCS, Brief Perceived Coercion Scale; ITAQ, Insight and Treatment Attitudes Questionnaire; SAI-E, Expanded Schedule for the Assessment of Insight; STAI, Spielberger State-Trait Anxiety Inventory; SUMD, Scale to Assess Unawareness of Mental Disorder; WCST, Wisconsin Card Sorting Test.

Table 4 Summary of individual interventional study findings (non-randomised controlled trials)

Intervention	Studies included	n	Outcome measure	Key finding	Quality (GRADE)
Altering presentation of material (5 studies)	Kennedy et al (2009) Reference Kennedy, Dornan, Rutledge, O'Neill and Kennedy45 Kleinman et al (1996) Reference Kleinman, Schachter, Jeffries and Goldhamer44 Munetz & Roth (1985) Reference Munetz and Roth42 Palmer et al (2002) Reference Palmer, Nayak, Dunn, Appelbaum and Jeste43 Wong et al (2000) Reference Wong, Clare, Holland, Watson and Gunn46	176	Change in capacity scores	Altering presentation of material associated with improved capacity	Low (−2 risk of bias)
Treatment as usual (antipsychotic medication) (2 studies)	Dornan et al (2015) Reference Dornan, Kennedy, Garland, Rutledge and Kennedy48 Owen et al (2011) Reference Owen, Ster, David, Szmukler, Hayward and Richardson47	237	Change in capacity scores	Treatment as usual (including antipsychotics) associated with improved capacity	Moderate (−2 risk of bias, +1 large effect)
Shared decision-making (2 studies)	Elbogen et al (2007) Reference Elbogen, Swanson, Appelbaum, Swartz, Ferron and Van Dorn38 Hamann et al (2011) Reference Hamann, Mendel, Meier, Asani, Pausch and Leucht49	442	Change in capacity scores	SDM improved capacity in one trial, but not in the other	Low (−1 risk of bias, −1 inconsistency)
Metacognitive training (1 study)	Naughton et al (2012) Reference Naughton, Nulty, Abidin, Davoren, O'Dwyer and Kennedy15	19	Change in capacity scores	MCT associated with improved capacity scores	Low (−1 risk of bias, −2 imprecision, +1 large effects)

MCT, metacognitive training; SDM, shared decision-making.

Meta-analysis

Psychotic symptoms

As shown in Fig. 2, pooled data from nine studies (n = 610) suggested there was a moderate to large negative association between total psychotic symptom severity, as assessed by total Brief Psychiatric Rating Scale (BPRS) or Positive and Negative Syndrome Scale (PANSS) scores, and the capacity of participants to understand information relevant to treatment decisions (r = −0.45, 95% CI −0.55 to −0.34; I ² = 60%, moderate quality evidence). All studies reported a negative correlation between symptom severity and understanding, although one reported a considerably smaller effect size. ^{Reference Grisso, Appelbaum and Hill-Fotouhi31} Removing this led to a slightly larger correlation and lower heterogeneity (r = −0.49, 95% CI −0.39 to −0.56; I ² = 46%). Data from six studies (n = 453) suggested there was a small correlation between overall symptoms and the ability of participants to appreciate information relevant to a treatment decision (r = −0.23, 95% CI −0.14 to −0.32; I ² = 0%, moderate quality evidence). According to data from seven studies (n = 528) there was a moderate correlation between total symptoms and the ability of participants to reason in relation to treatment decision-making (r = −0.31, 95% CI −0.48 to −0.12; I ² = 80%), but the quality of the evidence was judged to be low because of risk of bias and high heterogeneity. This high heterogeneity appeared to be attributable to the large correlation reported by a study of a forensic in-patient sample; ^{Reference Rutledge, Kennedy, O'Neill and Kennedy32} removing this study removed the heterogeneity and also lowered the effect size (r = −0.24, 95% CI −0.33 to −0.14; I ² = 0%).

Fig. 2 Association between total symptoms and (a) understanding; (b) appreciation; (c) reasoning. ES, effect size.

Depression

There was no evidence that depression was associated with the ability of participants to understand information about their treatment (Fig. 3; k = 3, n = 146; r = −0.04, 95% CI −0.20 to 0.13, I ² = 0%; moderate quality evidence).

Fig. 3 Association between depression and understanding. ES, effect size.

Cognitive and intellectual performance

Moderate to large associations were observed (Fig. 4) between verbal cognitive functioning (assessed using subtests from the Wechsler Adult Intelligence Scale) and the ability of participants to understand information relating to treatment decision-making (k = 4, n = 203; r = 0.42, 95% CI 0.20 to 0.60; I ² = 60%; low quality evidence) and to use reasoning (k = 3, n = 177; r = 0.39, 95% CI 0.26 to 0.51; I ² = 0%; low quality evidence).

Fig. 4 Association between verbal IQ score and (a) understanding; (b) reasoning. ES, effect size.

Education

Moderate-quality evidence suggested a large association between years spent in education and the ability of participants to understand information relating to treatment decisions (Fig. 5; k = 3, n = 201; r = 0.46, 95% CI 0.36 to 0.56; I ² = 0%). The association between years of education and participants' reasoning ability was small to moderate (k = 3, n = 201; r = 0.26, 95% CI 0.12 to 0.38; I ² = 0%; moderate quality evidence).

Fig. 5 Association between years of education and (a) understanding; (b) reasoning. ES, effect size.

Outcomes from individual studies

A full description of the results of individual studies is provided in online supplement DS6.

Executive functioning

One small study reported non-significant moderate correlations between domains of capacity and aspects of executive functioning, ^{Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33} whereas another reported large reductions in capacity in those with poor executive functioning. ^{Reference Mandarelli, Parmigiani, Tarsitani, Frati, Biondi and Ferracuti34}

Insight

Five studies assessed the relationship between capacity and different aspects of insight, ^{Reference Cairns, Maddock, Buchanan, David, Hayward and Richardson35–Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39} and generally found large reductions in capacity in those with poor insight. One of these studies used the Beck Cognitive Insight Scale, ^{Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39} and found much smaller and generally non-significant associations between capacity and self-certainty and self-reflectiveness, with the exception of reasoning and appreciation, which both had moderate positive correlations with self-reflectiveness (reasoning: r = 0.43, 95% CI 0.20 to 0.62; appreciation: r = 0.33, 95% 0.08 to 0.54;). Overall we judged the evidence on insight to be of moderate quality and consistent with the view that insight is associated with improved capacity, in particular reasoning ability.

Duration of illness

Two studies provided low-quality data on the relationship between duration of illness and capacity. ^{Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39,Reference Wong, Cheung and Chen40} One did not find a relationship, ^{Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39} whereas the other reported a small yet significant relationship with understanding (r = −0.24, 95% CI −0.02 to −0.44). ^{Reference Wong, Cheung and Chen40}

Metacognitive ability

One very small study found metacognitive ability was significantly associated with the understanding domain of capacity (r = 0.60, 95% CI 0.23 to 0.82). ^{Reference Koren, Poyurovsky, Seidman, Goldsmith, Wenger and Klein33}

Perceived coercion

Moderate-quality evidence from one study suggested that participants without capacity reported higher levels of perceived coercion (Mann–Whitney U = 422.5, P < 0.001). ^{Reference Cairns, Maddock, Buchanan, David, Hayward and Richardson35}

Anxiety

Moderate-quality evidence from two studies suggested state and trait anxiety might be positively associated with aspects of capacity, i.e. greater anxiety was linked to greater treatment decisional capacity. ^{Reference Capdevielle, Raffard, Bayard, Garcia, Baciu and Bouzigues36,Reference Raffard, Fond, Brittner, Bortolon, Macgregor and Boulenger39}

Interventions

Of the ten intervention studies we identified, five assessed the effect of altering the presentation of information on capacity, two examined the effect of usual treatment, two examined the effect of shared decision-making and one examined the effect of metacognitive training, which is a form of psychological intervention designed to improve a person's awareness of cognitive biases and thinking styles that may be involved in psychotic symptoms. ^{Reference Moritz, Woodward and Balzan41}

Presentation of material

Repetition of information, and discussion of presented information with others, were associated with significant large increases in capacity in two studies (d = 1.83, 95% CI 0.48 to 3.18; χ² = 12.05, P = 0.002), ^{Reference Munetz and Roth42,Reference Palmer, Nayak, Dunn, Appelbaum and Jeste43} whereas a non-significant, small improvement was reported by a third (d = 0.27, 95% CI −0.51 to 1.06). ^{Reference Kleinman, Schachter, Jeffries and Goldhamer44} However, Kennedy et al found that providing extra information to participants in a forensic setting was associated with a significant fell in capacity (d = 0.75, 95% CI 0.30 to 1.20), with a statistically significant proportion of the sample becoming incapable of making a treatment choice following the presentation of extra information. ^{Reference Kennedy, Dornan, Rutledge, O'Neill and Kennedy45} Wong et al successively simplified the presentation of information and found that as the task was simplified, capacity improved significantly (Cochran's Q = 14.4, d.f. = 3, P < 0.01). ^{Reference Wong, Clare, Holland, Watson and Gunn46} Overall, the risk of bias across these studies suggested the evidence was of low quality.

Usual treatment

Owen et al found that 37% of patients regained capacity following a month of treatment in hospital. ^{Reference Owen, Ster, David, Szmukler, Hayward and Richardson47} Dornan et al found that patients receiving treatment as usual, which included 25 hours per week of individual programmed activities as well as treatment with antipsychotic medications, improved on all domains of capacity: understanding d = 0.62 (95% CI 0.15 to 1.09); appreciation d = 0.39 (95% CI −0.07 to 0.85); reasoning d = 0.63 (95% CI 0.16 to 1.09). ^{Reference Dornan, Kennedy, Garland, Rutledge and Kennedy48} These authors also found that patients treated with clozapine had significantly larger improvements in appreciation than patients treated with other antipsychotic agents (d = 2.10, 95% CI 1.15 to 3.05), and smaller non-significant improvements were also observed for understanding (d = 0.75, 95% CI −0.09 to 1.59) and reasoning (d = 0.71, 95% CI −0.13 to 1.55). Overall, the evidence for the effect of usual treatment, including antipsychotic medication, was judged to be moderate in quality, with the risk of bias across the studies being mitigated by the large observed effects.

Shared decision-making

Two trials examined the effect of a shared decision-making intervention on capacity. However, these studies found conflicting results, meaning the overall estimate was low in quality. Elbogen et al found a significant effect of shared decision-making on reasoning (F _(1,355) = 4.30, P < 0.05) but not on appreciation or understanding, ^{Reference Elbogen, Swanson, Appelbaum, Swartz, Ferron and Van Dorn38} whereas Hamann et al found a non-significant small negative effect on capacity (d = −0.34, 95% CI −0.85 to 0.16). ^{Reference Hamann, Mendel, Meier, Asani, Pausch and Leucht49}

Metacognitive training

In a small uncontrolled study, Naughton et al found that patients who received group metacognitive training had significantly improved understanding (d = 1.44, 95% CI 0.42 to 2.45) and reasoning ability (d = 1.21, 95% CI 0.22 to 2.20), but there was no evidence of improvement in appreciation (d = 0.19, 95% CI −0.72 to 1.10). ^{Reference Naughton, Nulty, Abidin, Davoren, O'Dwyer and Kennedy15}