Reply to Moffitt et al.: Causal inference from observational data remains difficult

Abstract

As children, we are largely “stuck” with our parents, neighborhoods, and schools. Such forced environments are gradually left behind as we age, and our intelligence quotient (IQ) and “non-cognitive factors” (NCFs) (interests, personality, temperament, etc.) influence which new environments we are exposed to. Some of these are more cognitively demanding than others, causing IQs to change. If these same NCFs affect risks of early-onset cannabis use/dependence, this generates a correlation between IQ change and cannabis use.