Why include?
Inclusion of ethnic/racial minorities sustains the generalizability of the findings to the population as a whole and also makes subgroup analyses possible to determine influence of different ethnicities. Same holds good for women and older population. Metabolism of drugs, concurrent diseases and counter-indications vary between the two genders and also between different ethnicities \cite{Krecic_Shepard_2000}
Perceived Barriers
Results from meta analysis by Wendler et al. contradicted the widely held view that racial and ethnic minorities in the US were less willing to participate in clinical trials. While there was no significant difference between consent rates, they found substantial differences in race and ethnicity in the number of individuals invited to participate in trials \cite{Wendler_2005}
Increasing cost could be a potential barrier for recruitment. An analysis of two American studies showed that enrollment of women and ethnic minorities could double the cost of a trial \cite{Meinert1999}. Other hypotheses include language barriers, attitude of healthcare professionals leading to mistrust in minorities, disparities in socio‐economic position within and among different ethnic minority groups, cultural practices unique to some ethnicities that restrict participation \cite{Lee1999}\cite{Hussain_Gambles_2004}.
Older age
Cherubini et al extracted data from 251 ongoing clinical trials regarding heart failure from the World Health Organization Clinical Trials Registry, 25 % excluded patients from based on an arbitrary upper age limit. 43 % of the trials had one or more poorly exclusion criteria that could limit participation of older patients such as comorbidity described in a non-specific manner, use of medications that would not impact the study protocol, and visual and hearing impairment that would not lead to safety concerns \cite{Cherubini2011} \cite{Gurwitz2014}. Among 839 trials of Ischemic Heart Disease, Bourgeois et al showed that 53 % of trials excluded participants based on older age \cite{Bourgeois_2017}
Results derived from trials. Due to age related differences in pathophysiology of certain diseases, difference in pharmacokinetics and pharmacodynamics of drugs based on age that can impact tolerability and toxicity, data extrapolated from younger adults cannot be extrapolated to the elderly
\cite{Bourgeois2017}. While the FDA guidelines in 1989 stated that there is no clear basis to exclude participants based on age, the NIH revitalization Act of 1993 was limited to women and minorities and did not include provisions for older patients
https://www.fda.gov/regulatory-information/search-fda-guidance-documents/study-drugs-likely-be-used-elderly