Critical Appraisal informs us that:

  • Data extrapolated from small study samples are especially prone to error and bias.

  • Clinical trial researchers have a duty to recruit a sample of volunteers that closely represent the population under study to ensure its results are generalisable.


  • Minoritised ethnic populations are repeatedly underrepresented in research studies and trials.

  • Minoritised ethnic populations are disproportionately impacted by various conditions and illnesses.

How Underrepresentation impacts study validity:

External Validity

  • Sampling bias

  • Impact to generalisability - participants differ systematically from population under study

  • Missing racial categories - can not be applied to reader’s population

Internal Validity

  • Too-small sample sizes of minoritised ethnic populations can impact reliability as it leads to higher variability which may lead to bias

  • Evidence generated from small sample sizes is especially prone to error (false negatives/positives)

Examples of Underrepresentation in research:

  • Loree et al., 2019: Review of trials which led to FDA cancer drug approvals found Black population significantly underrepresented (22% of expected proportion). Race was only reported in 63% of trials

  • Murphy et al., 2016: Review of 209 US studies regarding mood and anxiety disorders. At least 38% no African Americans, 42% no race reported, 4% appropriate representation

  • Ding et al., 2021: Review of pivotal trials for dermatology drugs. Despite the varying population demographics of different countries and continents, where a study was conducted seemed to have minimal influence on the central tendency to predominantly enroll White participants.


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