Background
Recent efforts to reduce health inequities have failed to address the significant disparities that persist for some population groups in accessing high-quality care. One barrier to achieving health equity is the inadequate recruitment of under-represented and underserved populations in research [
1]. These research inequities contribute, in part, to the lack of evidence for providing effective care and treatment, resulting in evidence-biased care for some groups [
2]. There is increasing international recognition that populations included in clinical trials should adequately represent the population treated in clinical practice [
3], a position reinforced in the upcoming Clinical Trials Regulation No. 536/2014 that states that the participants in a clinical trial should represent the population groups that are likely to use the medicinal product investigated in the clinical trial [
4]. The lack of representation of certain groups in trial populations brings the external validity (the extent to which the results can be generalised to other circumstances or populations) [
5] of trials into question, which is even more important when these groups are systematically excluded from those trials [
6,
7]. This has led to major research funders, such as the UK National Institute for Health Research (NIHR), to lead projects to address the challenges of carrying out health research with under-represented groups (e.g. NIHR INCLUDE [
8]) and to introduce reviews of the suitability of, and justification for, inclusion and exclusion criteria as part of their review processes [
9].
Research involving vulnerable groups, such as adults lacking mental capacity, raises many ethical and legal issues—particularly with respect to informed consent for them to be included in a project [
10,
11]. As a result, recruitment of vulnerable groups to research is a complex process [
12,
13] and the exclusion of people with cognitive impairment from research is widespread [
6,
7]. The exclusion of those who lack the capacity to consent from participating in research has been highlighted as a concern in populations where the prevalence of impaired capacity is high [
14] and where less is known about what works most effectively to improve care [
15]. For example, the Learning Disabilities Mortality Review programme found that people with learning disabilities die, on average, 15–20 years earlier than the general population, with many deaths being potentially amenable to health care interventions [
16]. People living with a learning disability have higher rates of long-term health conditions, such as cardiovascular disease, diabetes and mental illness, and are more likely to be admitted to hospital as an emergency [
16]. However, there is a lack of an evidence base for many of the interventions and treatments provided to people with learning disabilities [
17]. Previous studies have found that over 90% of randomised controlled trials are designed to exclude people with a learning disability [
6]. A recent review of studies on the NIHR portfolio found that 60% of the studies excluded learning disability groups, none of the studies investigating pneumonia or sepsis included learning disability groups despite being a key contributor to premature deaths, and only 1.4% of all studies were specifically related to learning disabilities [
18]. Similar exclusions of people with cognitive impairment are seen in other areas of research such as geriatrics [
7], rehabilitation interventions following hip fracture [
19], peri-operative medicine [
20], trauma [
21] and neurological research [
22]. Under-recruitment to research into conditions such as dementia is one of the key challenges to advancing understanding of these conditions and improving the care and treatment of those who live with these conditions [
23].
With growing evidence of the widespread exclusion of adults lacking capacity from clinical trials and other research, there have been calls for a review of the ethical barriers to the inclusion of these populations, and for greater active involvement of research funding organisations to scrutinise the justifications behind this exclusion [
18]. However, this issue is more complex than might be first thought. The recruitment of adults with impaired capacity is situated within a complex system of factors [
24], and the differences between legal jurisdictions and how different types of research are governed within these jurisdictions adds further complexities [
2]. Research governance and funder oversight that focuses on ensuring that appropriate eligibility criteria are used will not be effective in increasing inclusivity in trials for adults who lack capacity unless the wider barriers to inclusion are recognised and addressed.
The exclusion of adults who lack capacity has been the subject of two recent publications in
Trials. In the first, we presented data on the concerningly low number of trials designed to include adults lacking capacity identified through an analysis of clinical trials in conditions commonly associated with cognitive impairment that were completed in the previous 3 years [
25]. The second was a response to our study, in which Griffiths et al. detailed the practical challenges encountered in developing their trial involving hard-to-reach groups of people living with dementia in the community, and the potential implications for being able to include those with impaired capacity [
26]—arguably the hardest of all the groups to reach. The barriers they described included gaining a favourable ethical opinion, designing recruitment pathways that ensure people living with dementia have the opportunity to participate in circumstances when their cognitive disability might impair their ability to read or understand an invitation letter, and the challenges of identifying consultees to be involved in decisions about their participation [
26].
This commentary discusses and expands on some of the issues raised by Griffiths et al., drawing on a non-systematic review of the literature, experience of conducting trials with populations with impaired capacity [
13,
27,
28], and recent findings from a series of studies exploring the involvement of adults who lack the capacity to consent [
25,
29‐
32]. The aim is to articulate for the first time some of the wider methodological, structural, and systemic barriers to the inclusion of adults lacking capacity as a first step towards identifying and addressing some of the potentially modifiable factors. This is presented from the perspective of trials conducted in the UK, but will have implications and relevance for research conducted in other legal jurisdictions.
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