On the causal interpretation of race in regressions adjusting for confounding and mediating variables

Abstract

We consider several possible interpretations of the "effect of race" when regressions are run with race as an exposure variable, controlling also for various confounding and mediating variables. When adjustment is made for socioeconomic status early in a person's life, we discuss under what contexts the regression coefficients for race can be interpreted as corresponding to the extent to which a racial inequality would remain if various socioeconomic distributions early in life across racial groups could be equalized. When adjustment is also made for adult socioeconomic status, we note how the overall racial inequality can be decomposed into the portion that would be eliminated by equalizing adult socioeconomic status across racial groups and the portion of the inequality that would remain even if adult socioeconomic status across racial groups were equalized. We also discuss a stronger interpretation of the effect of race (stronger in terms of assumptions) involving the joint effects of race-associated physical phenotype (eg, skin color), parental physical phenotype, genetic background, and cultural context when such variables are thought to be hypothetically manipulable and if adequate control for confounding were possible. We discuss some of the challenges with such an interpretation. Further discussion is given as to how the use of selected populations in examining racial disparities can additionally complicate the interpretation of the effects.

Figure 1

Diagram illustrating relations between physical phenotype (P), parental physical phenotype (PP), genetic background (G), family/parental socioeconomic status (SES₀), neighborhood socioeconomic status (NSES₀), history (H), and the outcome of interest Y

Figure 2

Diagram illustrating cultural context (C) that may be influenced by physical phenotype (P)

Figure 3

Diagram with physical phenotype, parental physical phenotype, genetic background and culutural context replaced by a race variable (R)

Figure 4

Diagram with adult socioeconomic status (SES₁) and the pathways from race components to the outcome (Y) through adult SES (the blue dotted pathways) and not through SES (the red dashed pathways)

Figure 5

Effects of race through adult SES (the blue dotted pathways) and not through SES (the red dashed pathways), with physical phenotype, parental physical phenotype, genetic background and culutural context replaced by a race variable (R)

Figure 6

Diagram illustrating bias in selected populations (S) in associations between race (R) and outcome (Y) that can result because of common causes of the variable defining the population (S) and the outcome (Y)