A term applied to the random assortment of alleles at the time of gamete formation, a process that results in population distributions of genetic variants that are generally independent of behavioral and environmental factors that typically confound epidemiologically derived associations between putative risk factors and disease. In some circumstances taking advantage of Mendelian randomization may provide an epidemiological study with the properties of a randomized comparison, for example, a randomized clinical trial. In particular, the use of Mendelian randomization may allow causal inferences to be drawn from epidemiological studies, typically using an instrumental variable estimator.