The lost and forgotten – Are some groups of people continually excluded from research?

September 2017


It is well-recognised that certain sectors of society are repeatedly underrepresented in research studies. Ethical guidelines for the inclusion of children, women and the cognitively impaired in research exist, but researchers tend to bias recruitment towards ‘normal’ people, applying the ‘one-size fits all’ approach to results and missing important physiological and psychological insights that could be gained from including a diverse group of individuals.

We should ask ourselves why certain groups, such as the elderly, ethnic minorities and people with a history of mental health, hearing impairment or complex comorbidities, are excluded in research: is the exclusion scientifically justified by the study (i.e. the evidence collected from the study can be generalised to all patients), or are they excluded because of the difficulty in managing vulnerable groups and the trouble and budget/ time constraints of going through research ethics committees’ applications? Although current ethical guidelines require a justification of both inclusion and exclusion groups, a recent review of trials on secondary prevention of cardiovascular disease found only one of 113 studies justified their exclusion criteria1.

Exclusion might, in some cases, be decided by the participant. For example, parents might not be comfortable with their children taking part in research, women of childbearing age might prefer to keep away from clinical trials and ethnic minorities might be reluctant to participate unless engaged through community support. In other cases, the inclusion criteria of the studies might be too restrictive. For example, a recent study found that depressed individuals included in antidepressant efficacy trials did not reflect the typical patient treated in clinical practice and 82% of depressed patients would have been excluded by the enrolment criteria2.

Excluding these groups from research comes with a range of implications: lack of sample diversity to be able to understand how the illness and treatment works, lack of information about the effectiveness of treatments across all members of society, and the potential danger of generalising the findings to those excluded groups which, in turn, might not even have access to treatment.

This has strong implications for adherence interventions and many ‘real world’ interventions may fail because we know that people who are the most ‘non-adherent’ might not partake in research. For example, a depressed patient has 1.76 times the odds of being non-adherent than a non-depressed patient3. Similarly, the most non-adherent groups to self-administered treatment for tuberculosis are prisoners, vulnerable migrants, homeless/people on temporary housing and people misusing alcohol or other substances4. It is likely that all these groups would be misrepresented (deliberately or not) in evidence-based adherence strategies.

Exclusion of patients from the developing world is another problem. For example, the difficulty of maintaining adherence rates to HIV medication in developed countries is well-documented5 but HIV-infected patients with the greatest adherence issues in those countries are repeatedly excluded from adherence intervention research even though this vulnerable group would benefit the most from these interventions6.


1 Schmidt, AF. et al. (2014). Justification of exclusion criteria was underreported in a review of cardiovascular trials. Journal of Clinical Epidemiology, 67(6):635-644.

2 Preskorn, SH, et al. (2015). How commonly used inclusion and exclusion criteria in antidepressant registration trials affect study enrollment. J Psychiatr Pract. 21(4):267-74.
3 Grenard, JL, et al. (2011). Depression and Medication Adherence in the Treatment of Chronic Diseases in the United States: A Meta-Analysis. Journal of General Internal Medicine, 26(10):1175-1182.
4 NICE. Tuberculosis in vulnerable groups. Local Government briefing [LGB11]. September 2013. 5 Bonolo PF, et al. (2008). Vulnerability and non-adherence to antiretroviral therapy among HIV patients Minas Gerais State, Brazil. Cad Saude Publica. 24:2603-2613.
6 Enriquez, M & McKinsey, DS (2011). Strategies to improve HIV treatment adherence in developed countries: clinical management at the individual level. HIV/AIDS. 3:45–51.