Methods for Ascertainment and Categorization of Race and Ethnicity for Clinical Research: An Overview of Reviews

The methods used to ascertain and categorize race and ethnicity in clinical research influence study design and may influence the interpretation and comparability of findings between studies. Use of inconsistent approaches across the literature may contribute to heterogeneity of findings, with some methods suggesting patterns not representative of underlying processes. This study aimed to systematically review methods used to ascertain race and ethnicity, evaluate systems of racial and ethnic categorization, and comparatively evaluate methods of ascertainment and categorization of race and ethnicity used in clinical research.

An umbrella review was conducted in accordance with the Joanna Briggs Institute (JBI) methodology for umbrella reviews and reported following Preferred Reporting Items for Overviews of Reviews (PRIOR) statement. We searched five databases (Ovid MEDLINE, Ovid Embase, CINAHL, Scopus, and Sociological Abstracts) from January 2002 to April 2025 using terms related to race and ethnicity, conceptualization, genetics, and clinical research. English-language review articles published in peer-reviewed journals were reviewed by at least two reviewers. Titles, abstracts, and full text articles were screened, and references of selected articles and grey literature. Data were abstracted using a standardized form, and further analyzed and summarised. A nonsystemic, purposive, environmental scan of the grey literature was included to capture representative examples of documents related to the study objectives.

The search generated 12,783 articles, with 139 review articles included. We identified six methods for the ascertainment of race and ethnicity: self-report, social assignment, name-based ethnic classification, geographic assignment, ancestry, and use of multimethod strategies. Twenty-one systems of categorization were identified, with racial categories ranging from 3 to 15. Terminology and systems of categorization varied both within and across geographic regions, reflecting population-specific contexts.

Self-report is the most common method of ascertainment; however alternative methods can be considered when self-reported data are not available. These methods capture different dimensions of race and ethnicity and should be selected and interpreted based on the research question and study context, rather than viewed as interchangeable. The variability in the categorization and terminology used for race and ethnicities suggests the need for informed use of these constructs, to support appropriate contextualization and interpretation of results. Improved methodologic consistency in the use of race and ethnicity is essential to strengthen the rigor of clinical research.