Ethnicity is used increasingly as a key variable to describe health data, and ethnic monitoring in the NHS will further stimulate this trend. We identify four fundamental problems with ethnicity in this type of research: the difficulties of measurement, the heterogeneity of the populations being studied, lack of clarity about the research purpose of the research, and ethnocentricity affecting the interpretation and use of data. Ethnicity needs to be used carefully to be a useful tool for health research. We make nine recommendations for future practice, one of which is that ethnicity and race should be recognised and treated as distinct concepts.

Epidemiology is the study of the distribution and determinants of disease. The main method of study, particularly for investigating the causes of disease, is to compare populations with different risks of disease. Ethnicity is a variable that is used increasingly to define populations for epidemiological studies. Differences by ethnicity in both the characteristics of populations and their experience of disease have been easy to describe, and the literature on ethnicity and health is large and growing.1 We consider here the nature of ethnicity, the attributes of sound epidemiological variables, the measurement and value of ethnicity as an epidemiological variable, and how ethnicity might best be used in future research. By reviewing critically ethnicity as a variable in epidemiology we hope to facilitate better research. This review is relevant to ethnic monitoring in the NHS.