et al., 2018) and educational attainment (Esch et al., 2014; Krapohl et al., 2014) are endogenous to a wide variety of other predictor variables. Given the wide variety of variables that predict tobacco use and educational attainment (Cheng & Furnham, 2021; Esch et al., 2014; Green et al., 2018; Krapohl et al., 2014), we expect that tobacco use and educational attainment are associated with unmeasured confounding variables. Furthermore, we expect that an array of measured variables will provide indirect insight into a wide variety of constructs beyond what is explicitly measured, provided that the observed confounders are proxies for the correlated error structure in the model driven by unmeasured factors. For example, if an unmeasured personality construct happens to be correlated with the measured variables included in the phenotypic PCs, the phenotypic PCs would index some amount of variance in this unmeasured construct, proportional to the correlations between measured variables and the unmeasured personality construct.
