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. Author manuscript; available in PMC: 2024 Apr 1.
Published in final edited form as: Addiction. 2022 Dec 7;118(4):739–749. doi: 10.1111/add.16088

FIGURE 3.

FIGURE 3

Mendelian randomization and the results. (a) The three fundamental instrumental variable (IV) assumptions in the Mendelian randomization (MR) analysis: (i) IVs are significantly associated with the exposure [i.e. smoking statuses (SS) or cigarettes per day (CPD)]; (ii) the exposure is not significantly associated with confounders of the exposure–outcome association; and (iii) IVs can affect the outcome variable only through the exposure. (b) The causal effect estimate with a 95% confidence interval using different MR methods for smoking traits SS and CPD separately, based on the IVs selected following the three IV assumptions. Gen-IVW (marked with a triangle) is the primary MR method (i.e. weighted generalized linear regression) and the other methods (marked with a dot) are the MR methods used in the sensitivity analysis. BAG = brain age gap