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. Author manuscript; available in PMC: 2020 Aug 1.
Published in final edited form as: Lancet Psychiatry. 2019 Nov 20;7(2):208–216. doi: 10.1016/S2215-0366(19)30293-7

Figure 1. Mendelian Randomization: comparisons and assumption.

Figure 1

1a Mendelian Randomization as a ‘natural’ Randomized Controlled Trial 

MR has been compared to a randomized controlled trial, with random allocation of genetic alleles at conception could be considered analogous to random allocation of interventions in a trial.

1b Assumptions in Mendelian Randomization 

MR assumes that the genetic variants are: a. associated with the exposure of interest; b. not associated with confounders; and c. only associated with the outcome through the exposure

1c Two-sample Mendelian Randomization 

Two-sample MR takes estimates of the SNP-exposure association from one population (e.g. a nutritional exposure GWAS) and the SNP-outcomes association from a separate sample (e.g. a psychiatric outcome GWAS).