What is already known on this topic

People with intellectual disability are frequently excluded from decision-making processes and not provided equal opportunity for informed consent, despite protections outlined in the United Nations Convention on the Rights of Persons with Disabilities.

People with intellectual disability have the capacity and desire to make informed medical decisions, which can improve their well-being, health satisfaction and health outcomes.

What this review study adds

Health professionals lack adequate training in valid informed consent and making reasonable adjustments for people with intellectual disability, and continue to perpetuate assumptions of incapacity.

Health information provided to people with intellectual disability is often inaccessible and insufficient for them to make informed decisions about healthcare.

The role of support people, systemic constraints, a person-centred approach and ineffective healthcare communication also affect informed consent.

How this review might affect research, practice or policy

Health professionals need additional training on how to provide a valid informed consent process for people with intellectual disability, specifically in using accessible health information, making reasonable adjustments (e.g., longer/multiple appointments, options of a support person attending or not, using plain English), involving the individual in discussions, and communicating effectively with them.

Inclusive research is needed to hear the voices and opinions of people with intellectual disability about healthcare decision-making and about informed consent practices in specific healthcare settings.

Introduction

Approximately 1% of the world’s population have intellectual disability.1 Intellectual disability is medically defined as a group of neurodevelopmental conditions beginning in childhood, with below average cognitive functioning and adaptive behaviour, including limitations in conceptual, social and practical skills.2 People with intellectual disability prefer an alternative strength-based definition, reflected in the comment by Robert Strike OAM (Order of Australia Medal): ‘We can learn if the way of teaching matches how the person learns’,3 reinforcing the importance of providing information tailored to the needs of a person with intellectual disability. A diagnosis of intellectual disability is associated with significant disparities in health outcomes.4–7 Person-centred decision-making and better communication have been shown to improve patient satisfaction,8 9 the physician–patient relationship10 and overall health outcomes11 for the wider population. Ensuring people with intellectual disability experience informed decision-making and accessible healthcare can help address the ongoing health disparities and facilitate equal access to healthcare.

Bodily autonomy is an individual’s power and agency to make decisions about their own body.12 Informed consent for healthcare enables a person to practice bodily autonomy and is protected, for example, by the National Safety and Quality Health Service Standards (Australia),13 Mental Capacity Act (UK)14 and the Joint Commission Standards (USA).15 In this article, we define informed consent according to three requirements: (1) the person is provided with information they understand, (2) the decision is free of coercion and (3) the person must have capacity.16 For informed consent to be valid, this process must be suited to the individual’s needs so that they can understand and communicate effectively. Capacity is the ability to give informed consent for a medical intervention,17 18 and the Mental Capacity Act outlines that ‘a person must be assumed to have capacity unless it is established that he lacks capacity’ and that incapacity can only be established if ‘all practicable steps’ to support capacity have been attempted without success.14 These assumptions of capacity are also decision-specific, meaning an individual’s ability to consent can change depending on the situation, the choice itself and other factors.17

Systemic issues with healthcare delivery systems have resulted in access barriers for people with intellectual disability,19 despite the disability discrimination legislation in many countries who are signatories to the United Nations (UN) Convention on the Rights of Persons with Disabilities.20 Patients with intellectual disability are not provided the reasonable adjustments that would enable them to give informed consent for medical procedures or interventions,21 22 despite evidence that many people with intellectual disability have both the capacity and the desire to make their own healthcare decisions.21 23

To support people with intellectual disability to make independent health decisions, an equitable and accessible informed consent process is needed.24 However, current health systems have consistently failed to provide this.21 25 To address this gap, we must first understand the factors that contribute to inequitable and inaccessible consent. To the best of our knowledge, the only current review of informed consent for people with intellectual disability is an integrative review by Goldsmith et al.26 Many of the included articles focused on assessment of capacity27–29 and research consent.30–32 The review’s conclusion supported the functional approach to assess capacity, with minimal focus on how the informed consent processes can be improved. More recently, there has been a move towards ensuring that the consent process is accessible for all individuals, including elderly patients33 and people with aphasia.34 However, there remains a paucity of literature about the informed consent process for people with intellectual disability, with no systematic reviews summarising the factors influencing the healthcare consent process for people with intellectual disability.

Aims

To identify barriers to and enablers of the informed healthcare consent process for people with intellectual disability, and to understand how this can be made equitable and accessible.

Methods

A systematic literature review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols (PRISMA-P) systematic literature review protocol.35 The PRISMA 2020 checklist36 and ENhancing Transparency in REporting the synthesis of Qualitative research (ENTREQ) reporting guidelines were also followed.37 The full study protocol is included in online supplemental appendix 1.

No patients or members of the public were involved in this research for this manuscript.

Search strategy

A search strategy was developed to identify articles about intellectual disability, consent and healthcare interventions, described in online supplemental appendix 2. Multiple databases were searched for articles published between January 1990 to January 2022 (Embase, MEDLINE, PsychINFO, PubMed, SCOPUS, Web of Science and CINAHL). These databases include healthcare and psychology databases that best capture relevant literature on this topic, including medical, nursing, social sciences and bioethical literature. The search was limited to studies published from 1990 as understandings of consent have changed since then.38 39 This yielded 4853 unique papers which were imported into Covidence, a specialised programme for conducting systematic reviews.40

Study selection

Citation screening by abstract and titles was completed by two independent researchers (MD and EEP). Included articles had to:

Examine the informed consent process for a healthcare intervention for people with intellectual disability.

Have collected more than 50% of its data from relevant stakeholders, including adults with intellectual disability, families or carers of a person with intellectual disability, and professionals who engage with people with intellectual disability.

Report empirical data from primary research methodology.

Be published in a peer-reviewed journal after January 1990.

Be available in English.

Full text screening was completed by two independent researchers (MD and EEP). Articles were excluded if consent was only briefly discussed or if it focused on consent for research, capacity assessment, or participant knowledge or comprehension. Any conflicts were resolved through discussion with an independent third researcher (IS).

Additional studies were identified through an ancestral search and by hand-searching three major journals relevant to intellectual disability research. Journals were selected if they had published more than one included article for this review or in previous literature reviews conducted by the research team.

Quality assessment

Two independent researchers (MD and IS) assessed study quality with the QualSyst tool,41 which can assess both qualitative and quantitative research papers. After evaluating the distribution of scores, a threshold value of 55% was used, as suggested by QualSyst41 to exclude poor-quality studies but capture enough studies overall. Any conflicts between the quality assessment scores were resolved by a third researcher (EEP). For mixed-method studies, both qualitative and quantitative quality scores were calculated, and the higher value used.

Data collection

Two independent researchers (MD and JH) reviewed each study and extracted relevant details, including study size, participant demographics, year, country of publication, study design, data analysis and major outcomes reported. Researchers used standardised data collection forms designed, with input from senior researchers with expertise in qualitative research (IS and EEP), to extract data relevant to the review’s research aims. The form was piloted on one study, and a second iteration made based on feedback. These forms captured data on study design, methods, participants, any factors affecting the process of informed consent and study limitations. Data included descriptions and paragraphs outlining key findings, the healthcare context, verbatim participant quotes and any quantitative analyses or statistics. Missing or unclear data were noted.

Data analysis

A pilot literature search showed significant heterogeneity in methodology of studies, limiting the applicability of traditional quantitative analysis (ie, meta-analysis). Instead, inductive thematic analysis was chosen as an alternative methodology42 43 that has been used in recent systematic reviews examining barriers and enablers of other health processes.44 45 The six-phase approach described by Braun and Clarke was used.46 47 A researcher (MD) independently coded the extracted data of each study line-by-line, with subsequent data grouped into pre-existing codes or new concepts when necessary. Codes were reviewed iteratively and grouped into categories, subthemes and themes framed around the research question. Another independent researcher (JH) collated and analysed the data on study demographics, methods and limitations. The themes were reviewed by two senior researchers (EEP and IS).

Qualitative methods of effect size calculations have been described in the literature,48 49 which was captured in this review by the number of studies that identified each subtheme, with an assigned frequency rating to compare their relative significance. Subthemes were given a frequency rating of A, B, C or D if they were identified by >10, 7–9, 4–6 or <3 articles, respectively. The overall significance of each theme was estimated by the number of studies that mentioned it and the GRADE framework, a stepwise approach to quality assessment using a four-tier rating system. Each study was evaluated for risk of bias, inconsistency, indirectness, imprecision and publication bias.50 51 Study sensitivity was assessed by counting the number of distinct subthemes included.52 The quality of findings was designated high, moderate or low depending on the frequency ratings, the QualSyst score and the GRADE scores of studies supporting the finding. Finally, the relative contributions of each study were evaluated by the number of subthemes described, guided by previously reported methods for qualitative reviews.52

Co-research

The findings were reviewed by two co-researchers with intellectual disability (JL and SS), with over 30 years combined experience as members and employees of a self-advocacy organisation. Guidance on the findings and an easy read summary was produced in line with best-practice inclusive research53 54 over multiple discussions. Input from two health professional researchers (MD and EEP) provided data triangulation and sense-checking of findings.

Results

Twenty-three articles were identified (figure 1): 14 qualitative, 6 quantitative and 3 mixed-methods. Two papers included the same population of study participants: McCarthy55 and McCarthy,56 but had different research questions. Fovargue et al 57 was excluded due to a quality score of 35%. Common quality limitations were a lack of verification procedures to establish credibility and limited researcher reflexivity. No studies were excluded due to language requirements (as all were in English) or age restrictions (all studies had majority adult participants).

Figure 1

PRISMA 2020 flowchart for the systematic review.36

Studies were published from 1999 to 2020 and involved participant populations from the UK (n=18), USA (n=3), Sweden (n=1) and Ireland (n=1). Participant numbers ranged from 9 to 604 (median 21), and participants included people with intellectual disability (n=817), health professionals (n=272), carers and support people (n=48), and other professionals that work with people with intellectual disability (n=137, community service agency directors, social workers, administrative staff and care home staff). Ages of participants ranged from 8 to 84 years, though only Aman et al 58 included participants <18 years of age. This study was included as the article states very few children were included. Studies examined consent in different contexts, including contraception and sexual health (6/23 articles),58–60 medications (5/23 articles),58–62 emergency healthcare,63 cervical screening,64 community referrals,58–61 65 mental health,66 hydrotherapy,64 blood collection67 and broad decision-making consent without a specific context.65 68–71 A detailed breakdown of each study is included in online supplemental appendix 3.

Six major themes were identified from the studies, summarised in figure 2. An overview of included studies showing study sensitivity, effect size, QualSyst and GRADE scores is given in online supplemental appendix 4. Studies with higher QualSyst and GRADE scores contributed more to this review’s findings and tended to include more subthemes; specifically, Rogers et al,66 Sowney and Barr,63 Höglund and Larsson,72 and McCarthy55 and McCarthy.56 Figure 3 gives the easy read version of theme 1, with the full easy read summary in online supplemental appendix 5.

Figure 2

Summary of the identified six themes and subthemes.

Figure 3

Theme 1 of the easy read summary.

Theme 1—Health professionals’ attitudes and lack of education about informed consent

Health professionals’ attitudes and practices were frequently (18/21) identified as factors affecting the informed consent process, with substantial evidence supporting this theme. Studies noted the lack of training for health professionals in supporting informed consent for people with intellectual disability, their desire for further education, and stereotypes and discrimination perpetuated by health professionals.

Lack of health professional education on informed consent and disability discrimination legislation

Multiple studies reported inconsistent informed consent practices, for various reasons: some reported that health professionals ‘forgot’ to or ‘did not realise consent was necessary’,63 73 but inconsistent consent practices were also attributed to healthcare providers’ unfamiliarity with consent guidelines and poor education on this topic. Carlson et al 73 reported that only 44% of general practitioners (GPs) were aware of consent guidelines, and there was the misconception that consent was unnecessary for people with intellectual disability. Similarly, studies of psychologists66 and nurses63 found that many were unfamiliar with their obligations to obtain consent, despite the existence of anti-discrimination legislation. People with intellectual disability describe feeling discriminated against by health professionals, reflected in comments such as ‘I can tell, my doctor just thinks I’m stupid – I'm nothing to him’.74 Poor consent practices by health professionals were observed in Goldsmith et al,67 while health professionals surveyed by McCarthy56 were unaware of their responsibility to provide accessible health information to women with intellectual disability. Improving health professional education and training was suggested by multiple studies as a way to remove this barrier.63 65–67 69 73

Lack of training on best practices for health professions caring for people with intellectual disability

A lack of training in caring for and communicating with people with intellectual disability was also described by midwives,72 psychologists,66 nurses,63 pharmacists61 and GPs.56 72 75 Health professionals lacked knowledge about best practice approaches to providing equitable healthcare consent processes through reasonable adjustments such as accessible health information,56 60 66 longer appointments times,60 72 simple English62 67 and flexible approaches to patient needs.63 72

Health professionals’ stereotyping and assumptions of incapacity

Underlying stereotypes contributed to some health professionals’ (including nurses,63 GPs56 and physiotherapists64) belief that people with intellectual disability lack capacity and therefore, do not require opportunities for informed consent.56 64 In a survey of professionals referring people with intellectual disability to a disability service, the second most common reason for not obtaining consent was ‘patient unable to understand’.73

Proxy consent as an inappropriate alternative

People with intellectual disability are rarely the final decision-maker in their medical choices, with many health providers seeking proxy consent from carers, support workers and family members, despite its legal invalidity. In McCarthy’s study (2010), 18/23 women with intellectual disability said the decision to start contraception was made by someone else. Many GPs appeared unaware that proxy consent is invalid in the UK.56 Similar reports came from people with intellectual disability,55 56 60 64 69 76 health professionals (nurses, doctors, allied health, psychologists),56 63 64 66 77 support people64 77 and non-medical professionals,65 73 and capacity was rarely documented.56 62 77

Exclusion of people with intellectual disability from decision-making discussions

Studies described instances where health professionals made decisions for their patients with intellectual disability or coerced patients into a choice.55 72 74 76 77 In Ledger et al 77, only 62% of women with intellectual disability were involved in the discussion about contraception, and only 38% made the final decision, and others stated in Wiseman and Ferrie74: ‘I was not given the opportunity to explore the different options. I was told what one I should take’. Three papers outlined instances where the choices of people with intellectual disability were ignored despite possessing capacity65 66 69 and when a procedure continued despite them withdrawing consent.69

Theme 2—Inadequate accessible health informationLack of accessible health information

The lack of accessible health information was the most frequently identified subtheme (16/23 studies). Some studies reported that health professionals provided information to carers instead,60 avoided providing easy read information due to concerns about ‘offending’ patients75 or only provided verbal information.56 67 Informed consent was supported when health professionals recognised the importance of providing medical information64 and when it was provided in an accessible format.60 Alternative approaches to health information were explored, including virtual reality68 and in-person education sessions,59 with varying results. Overall, the need to provide information in different formats tailored to an individual’s communication needs, rather than a ‘one size fits all’ approach, was emphasised by both people with intellectual disability60 and health professionals.66

Insufficient information provided

Studies described situations where insufficient information was provided to people with intellectual disability to make informed decisions. For example, some people felt the information from their GP was often too basic to be helpful (Fish et al 60) and wanted additional information on consent forms (Rose et al 78).

Theme 3—The involvement of support people

Support people (including carers, family members and group home staff) were identified in 11 articles as both enablers of and barriers to informed consent. The antagonistic nature of these findings and lower frequency of subthemes are reflected in the lower quality assessments of evidence.

Support people facilitated communication with health professionals

Some studies reported carers bridging communication barriers with health to support informed consent.63 64 McCarthy56 found 21/23 of women with intellectual disability preferred to see doctors with a support person due to perceived benefits: ‘Sometimes I don’t understand it, so they have to explain it to my carer, so they can explain it to me easier’. Most GPs in this study (93%) also agreed that support people aided communication.

Support people helped people with intellectual disability make decisions

By advocating for people with intellectual disability, carers encouraged decision-making,64 74 provided health information,74 77 emotional support76 and assisted with reading or remembering health information.55 58 76 Some people with intellectual disability explicitly appreciated their support person’s involvement,60 such as in McCarthy’s55 study where 18/23 participants felt supported and safer when a support person was involved.

Support people impeded individual autonomy

The study by Wiseman and Ferrie74 found that while younger participants with intellectual disability felt family members empowered their decision-making, older women felt family members impaired their ability to give informed consent. This was reflected in interviews with carers who questioned the capacity of the person with intellectual disability they supported and stated they would guide them to pick the ‘best choice’ or even over-ride their choices.64 Studies of psychologists and community service directors described instances where the decision of family or carers was prioritised over the wishes of the person with intellectual disability.65 66 Some women with intellectual disability in McCarthy’s studies (2010, 2009)55 56 appeared to have been coerced into using contraception by parental pressures or fear of losing group home support.

Theme 4—Systemic constraints within healthcare systemsTime restraints affect informed consent and accessible healthcare

Resource limitations create time constraints that impair the consent process and have been identified as a barrier by psychologists,66 GPs,56 hospital nurses63 and community disability workers.73 Rogers et al 66 highlighted that a personalised approach that could improve informed decision-making is restricted by inflexible medical models. Only two studies described flexible patient-centred approaches to consent.60 72 A survey of primary care practices in 2007 reported that most did not modify their cervical screening information for patients with intellectual disability because it was not practical.75

Inflexible models of consent

Both people with intellectual disability76 and health professionals66 recognised that consent is traditionally obtained through one-off interactions prior to an intervention. Yet, for people with intellectual disability, consent should ideally be an ongoing process that begins before an appointment and continues between subsequent ones. Other studies have tended to describe one-off interactions where decision-making was not revisited at subsequent appointments.56 60 72 76

Lack of systemic supports

In one survey, self-advocates highlighted a lack of information on medication for people with intellectual disability and suggested a telephone helpline and a centralised source of information to support consent.60 Health professionals also want greater systemic support, such as a health professional specialised in intellectual disability care to support other staff,72 or a pharmacist specifically to help patients with intellectual disability.61 Studies highlighted a lack of guidelines about healthcare needs of people with intellectual disabilities such as contraceptive counselling72 or primary care.75

Theme 5—Person-centred informed consent

Ten studies identified factors related to a person-centred approach to informed consent, grouped below into three subthemes. Health professionals should tailor their practice when obtaining informed consent from people with intellectual disability by considering how these subthemes relate to the individual. Each subtheme was described five times in the literature with a relative frequency rating of ‘C’, contributing to overall lower quality scores.

Previous experience with decision-making

Arscott et al 71 found that the ability of people with intellectual disability to consent changed with their verbal and memory skills and in different clinical vignettes, supporting the view of ‘functional’ capacity specific to the context of the medical decision. Although previous experiences with decision-making did not influence informed consent in this paper, other studies suggest that people with intellectual disability accustomed to independent decision-making were more able to make informed medical decisions,66 70 and those who live independently were more likely to make independent healthcare decisions.56 Health professionals should be aware that their patients with intellectual disability will have variable experience with decision-making and provide individualised support to meet their needs.

Variable awareness about healthcare rights

Consent processes should be tailored to the health literacy of patients, including emphasising available choices and the option to refuse treatment. In some studies, medical decisions were not presented to people with intellectual disability as a choice,64 and people with intellectual disability were not informed of their legal right to accessible health information.56

Power differences and acquiescence

Acquiescence by people with intellectual disability due to common and repeated experiences of trauma—that is, their tendency to agree with suggestions made by carers and health professionals, often to avoid upsetting others—was identified as an ongoing barrier. In McCarthy’s (2009) interviews with women with intellectual disability, some participants implicitly rejected the idea that they might make their own healthcare decisions: ‘They’re the carers, they have responsibility for me’. Others appeared to have made decisions to appease their carers: ‘I have the jab (contraceptive injection) so I can’t be blamed for getting pregnant’.55 Two studies highlighted that health professionals need to be mindful of power imbalances when discussing consent with people with intellectual disability to ensure the choices are truly autonomous.61 66

Theme 6—Effective communication between health professionals and patientsImplementation of reasonable adjustments for verbal and written information

Simple language was always preferred by people with intellectual disability.60 67 Other communication aids used in decision-making included repetition, short sentences, models, pictures and easy read brochures.72 Another reasonable adjustment is providing the opportunity to ask questions, which women with intellectual disability in McCarthy’s (2009) study reported did not occur.55

Tailored communication methods including non-verbal communication

Midwives noted that continuity of care allows them to develop rapport and understand the communication preferences of people with intellectual disability.72 This is not always possible; for emergency nurses, the lack of background information about patients with intellectual disability made it challenging to understand their communication preferences.63 The use of non-verbal communication, such as body language, was noted as underutilised62 66 and people with intellectual disability supported the use of hearing loops, braille and sign language.60

Discussion

To the best of our knowledge, this is the first systematic review investigating the barriers and enablers of the informed consent process for healthcare procedures for people with intellectual disability. The integrative review by Goldsmith et al 26 examined capacity assessment and shares only three articles with this systematic review.69 71 73 Since the 2000s, there has been a paradigm shift in which capacity is no longer considered a fixed ability that only some individuals possess38 39 but instead as ‘functional’: a flexible ability that changes over time and in different contexts,79 reflected in Goldsmith’s review. An individual’s capacity can be supported through various measures, including how information is communicated and how the decision-making process is approached.18 80 By recognising the barriers and enablers identified in this review, physicians can help ensure the consent process for their patients with intellectual disability is both valid and truly informed. This review has highlighted the problems of inaccessible health information, insufficient clinical education on how to make reasonable adjustments and lack of person-centred trauma-informed care.

Recommendations

Health professionals require training in the informed consent process for people with intellectual disability, particularly in effective and respectful communication, reasonable adjustments and trauma-informed care. Reasonable adjustments include offering longer or multiple appointments, using accessible resources (such as easy read information or shared decision-making tools) and allowing patient choices (such as to record a consultation or involve a support person). Co-researchers reported that many people with intellectual disability prefer to go without a support person because they find it difficult to challenge their decisions and feel ignored if the health professional only talks to the support person. People with intellectual disability also feel they cannot seek second opinions before making medical decisions or feel pressured to provide consent, raising the possibility of coercion. These experiences contribute to healthcare trauma. Co-researchers raised the importance of building rapport with the person with intellectual disability and of making reasonable adjustments, such as actively advocating for the person’s autonomy, clearly stating all options including the choice to refuse treatment, providing opportunities to contribute to discussions and multiple appointments to ask questions and understand information. They felt that without these efforts to support consent, health professionals can reinforce traumatic healthcare experiences for people with intellectual disability. Co-researchers noted instances where choices were made by doctors without discussion and where they were only given a choice after requesting one and expressed concern that these barriers are greater for those with higher support needs.

Co-researchers showed how these experiences contributed to mistrust of health professionals and poorer health outcomes. In one situation, a co-researcher was not informed of a medication’s withdrawal effects, resulting in significant side-effects when it was ceased. Many people with intellectual disability describe a poor relationship with their health professionals, finding it difficult to trust health information provided due to previous traumatic experiences of disrespect, coercion, lack of choice and inadequate support. Many feel they cannot speak up due to the power imbalance and fear of retaliation. Poor consent practices and lack of reasonable adjustments directly harm therapeutic alliances by reducing trust, contribute to healthcare trauma and lead to poorer health outcomes for people with intellectual disability.

Additional education and training for health professionals is urgently needed in the areas of informed consent, reasonable adjustments and effective communication with people with intellectual disability. The experiences of health professionals within the research team confirmed that there is limited training in providing high-quality healthcare for people with intellectual disability, including reasonable adjustments and accessible health information. Co-researchers also suggested that education should be provided to carers and support people to help them better advocate for people with intellectual disability.

Health information should be provided in a multimodal format, including written easy read information. Many countries have regulation protecting the right to accessible health information and communication support to make an informed choice, such as UK’s Accessible Information Standard,81 and Australia’s Charter of Health Care Rights,24 yet these are rarely observed. Steps to facilitate this include routinely asking patients about information requirements, system alerts for an individual’s needs or routinely providing reasonable adjustments.82 Co-researchers agreed that there is a lack of accessible health information, particularly about medications, and that diagrams and illustrations are underutilised. There is a critical need for more inclusive and accessible resources to help health professionals support informed consent in a safe and high-quality health system. These resources should be created through methods of inclusive research, such as co-production, actively involving people with intellectual disability in the planning, creation, and feedback process.53

Strengths and limitations

This systematic review involved two co-researchers with intellectual disability in sense-checking findings and co-creating the easy read summary. Two co-authors who are health professionals provided additional sense-checking of findings from a different stakeholder perspective. In future research, this could be extended by involving people with intellectual disability in the design and planning of the study as per recommendations for best-practice inclusive research.53 83

The current literature is limited by low use of inclusive research practices in research involving people with intellectual disability, increasing vulnerability to external biases (eg, inaccessible questionnaires, involvement of carers in data collection, overcompliance or acquiescence and absence of researcher reflexivity). Advisory groups or co-research with people with intellectual disability were only used in five studies.58 60 68 74 76 Other limitations include unclear selection criteria, low sample sizes, missing data, using gatekeepers in patient selection and predominance of UK-based studies—increasing the risk of bias and reducing transferability. Nine studies (out of 15 involving people with intellectual disability) explicitly excluded those with severe or profound intellectual disability, reflecting a selection bias; only one study specifically focused on people with intellectual disability with higher support needs. Studies were limited to a few healthcare contexts, with a focus on consent about sexual health, contraception and medications.

The heterogeneity and qualitative nature of studies made it challenging to apply traditional meta-analysis. However, to promote consistency in qualitative research, the PRISMA and ENTREQ guidelines were followed.36 37 Although no meta-analyses occurred, the duplication of study populations in McCarthy 2009 and 2010 likely contributed to increased significance of findings reported in both studies. Most included studies (13/23) were published over 10 years ago, reducing the current relevance of this review’s findings. Nonetheless, the major findings reflect underlying systemic issues within the health system, which are unlikely to have been resolved since the articles were published, as the just-released final report of the Australian Royal Commission into Violence, Abuse, Neglect and Exploitation of People with Disability highlights.84 There is an urgent need for more inclusive studies to explore the recommendations and preferences of people with intellectual disability about healthcare choices.

Conclusion

Informed consent processes for people with intellectual disability should include accessible information and reasonable adjustments, be tailored to individuals’ needs and comply with consent and disability legislation. Resources, guidelines and healthcare education are needed and should cover how to involve carers and support people, address systemic healthcare problems, promote a person-centred approach and ensure effective communication. These resources and future research must use principles of inclusive co-production—involving people with intellectual disability at all stages. Additionally, research is needed on people with higher support needs and in specific contexts where informed consent is vital but under-researched, such as cancer screening, palliative care, prenatal and newborn screening, surgical procedures, genetic medicine and advanced therapeutics such as gene-based therapies.

Data availability statement

Data are available upon reasonable request. Additional data and materials such as data collection forms, data extraction and analysis templates and QualSyst assessment data can be obtained by contacting the corresponding author.

Ethics statementsPatient consent for publication

Not applicable.

Ethics approval

Not applicable.