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. Author manuscript; available in PMC: 2018 Mar 1.
Published in final edited form as: Curr Environ Health Rep. 2017 Mar;4(1):44–50. doi: 10.1007/s40572-017-0122-7

Figure 2.

Figure 2

Variables with solid outlines are observed; those with dashed outlines are unobserved. X represents one or more covariates that could potentially affect serum lipid levels (arrow 1), overall exposure (arrow 2), and/or the outcome (arrow 3). Examples of X include age, sex, BMI, and race. (Reproduced from: O’Brien et al., 2016;124(2):220-7, with permission from Environmental Health Perspectives) [5••].