Ethnicity in Stroke: Practical Implications

To the Editor: I read with interest the editorial of Drs Fustinoni and Biller on ethnicity and stroke.1 The authors give several examples to demonstrate the dark side of “ethnicity” as an epidemiological variable. I agree that ethnicity is a complex, inherently heterogeneous concept influenced by different cultural and socioeconomic factors.2 The authors make the point that ethnicity is neither precise nor easily measured. However, I would like to discuss some issues of potential interest. First, ethnicity is derived from a Greek word meaning “population” or “tribe.” The criteria to define ethnicity have varied worldwide during the past decades. Therefore, criteria to classify ethnic groups may vary from one country to another.2,3 It is well known that most classifications have a bias. However, it is crucial to identify population subgroups to easily recognize and differentiate risk factors and, subsequently, patterns of disease. Thus, classifications are necessary in clinical practice and research, even if not perfect. It is the duty of the clinical investigator to use the most precise definition possible. Ethnic groups may be classified by using different criteria, such as geographic origin; migratory status; selfdefined, past generation criteria; and tribe origin, among others. In addition, ethnicity depends on the context in which the definition is made.4 The same criteria are not necessarily valid for different countries. Second, the authors mention that “ethnic categories are usually not defined in scientific reports, which results in dubious findings that are difficult to compare.” Of course, poorly defined groups will contribute more confusion than clarification to a given topic. However, the existence of poorly designed studies does not justify the elimination of all data derived from other good reports. Third, Fustinoni and Biller cite questionable examples that have been used to criticize ethnicity, such as, “What is black to someone from the United States may be white to a Brazilian or a Caribbean islander.” This type of extreme confusion is unlikely to arise in practice. Although relativity should be taken in consideration to avoid simplistic conclusions, citing the geographic or tribe origin of such ethnic groups may help to individualize their underlying characteristics (eg, natives from Brazil, pygmies from South Africa). Other authors have used erroneous definitions of ethnicity including skin color, phenotype, and socioeconomic characteristics.3–5 Moreover, ethnicity has erroneously been used as a synonym of race. All these variables are unquestionably related to ethnicity, but should not be used to define it. Additional confusion ensues when authors leave in the hands of the individuals studied the decision for their own classification (self-defined ethnicity) or use the family’s surname.3,6 Some journals have recommendations to describe ethnicity.2,7 Thus, there have been published guidelines on the use of race, ethnicity, and culture descriptions in an attempt to consistently measure all of them.7 The more descriptive the definition of ethnicity, the more reliable the classification for a given population. Fourth, to my understanding, the authors transmit a negative perception of ethnicity as an epidemiological variable and use confusing examples to validate their opinion. They mention that “the consequences of flawed ethnicity research may lead to the assumption that ethnic minorities are an unhealthy social burden, that there are ‘ethnic’ diseases which separate specific groups. . . , and that whites are the gold standard of health.” This statement manifests the existing confusion between race and ethnicity and may be misinterpreted by the readers. Fifth, most criticisms of ethnicity may apply to other frequently used epidemiological variables. In terms of clinical epidemiology, ethnic populations are mostly heterogeneous and influenced by important confounders (eg, socioeconomic status). However, its heterogeneous quality does not imply that there is “nothing that could be done” or that the ethnic differences in such a population should be ignored. Most epidemiologists recommend describing ethnic backgrounds.2,3,8,9 Senior and Bophal2 give several suggestions on how to make ethnicity a reliable epidemiological variable. Time and place of origin are necessary to better understand the subgroup of interest.3,9 Comparison between subgroups from one region to another may be possible if thoroughly descriptive criteria are known and used. In other words, what would be questionable is the generalizability (external validity of the study) but not the concept of ethnicity.10 The goal of an epidemiological study should be to analyze an appropriately defined ethnic subgroup within a population, with its specific risk factors, to predict the pattern of a disease. As a result, preventive strategies could be considered to reduce the stroke incidence in such population. Preventive measures for one ethnically defined population may be different from those for others. For example, it has been suggested in descriptive studies that native people (individuals born in South American countries without European origin) from South America have a higher frequency of hemorrhagic stroke and penetrating small-artery disease. Certainly, prospective studies would be necessary to determine whether native people from different South American countries have the same risk factors and stroke subtypes. Thus, ignoring the concept of ethnicity will limit our knowledge of these important findings and, subsequently, the opportunity to implement appropriately distributed preventive strategies. Finally, our goal should be to detect properly designed studies in which ethnic groups are adequately defined. A clarifying article; even in controversial scenarios, should include some recommendation, suggestions, or guidelines. If not, the authors translate their own uncertainty to readers. This is ultimately a defeatist and unproductive attitude. As former French President de Gaulle said, “Do you bring solutions or are you part of the problem?” Ethnicity is a necessary epidemiological variable for differentiating subgroups of individuals within a population who share disease variables different from those in other people within the same population. Recognizing the value of ethnicity will improve our knowledge of stroke epidemiology.