 Our discussion thus far has implicitly proceeded on the assumption that inequalities in health are defined in terms of membership in some social group or other. An “inequality” in health, so defined, is a difference between the health status of two groups, with the identity of the group following from the choice of the social variable with which health is correlated. For example, we note above that in 2019, the life expectancy was 78.8 years for non-Hispanic white Americans, and 74.7 years for non-Hispanic Black Americans. While this is how most of the discussion in the literature on health inequalities is actually structured, the definition is controversial. Notably, Murray, Gakidou, and Frenk (1999: 537) argue in favor of an alternative methodology, in which “health inequality” refers to “the variation in health status across individuals in a population”, rather than to a difference in health status between social groups.