Racial/ethnic minorities:
In a cohort free of CHD, there was no significant difference in the prevalence of dyslipidemia between blacks, Hispanics and non Hispanic whites. However the Hispanics were 20 % less likely to report drug therapy and blacks 15 % less likely . Also, these groups were 30 % less likely to have their lipids under control than their non Hispanic white counterparts \cite{Goff_2006}\cite{Leigh_2016}. The report by Jacobs et al \cite{Jacobs_2005} also noted that among patients with DM, Hispanics and African Americans were less likely to have LDL at goal compared to Caucasian population.
Prevalence of DM was lowest among non Hispanic whites at 7.5 % and highest among AI/AN at 16 %, this was 11% and 9 % in Blacks and Asians respectively. These statistics are percentages within each race/ethnicity and do not represent their percentage share in the entire disease burden. However given that they constitute nearly 40 % of the US population
https://www.census.gov/data/tables/2017/demo/popproj/2017-summary-tables.html , they make a substantial part of the disease burden, thus signifying an under-representation in trials. For instance, in our study, Blacks formed only 2 % of the study population in CHD trials, and 5 % of the DM cohort.
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}.