Reproducibility has long been considered a key part of the scientific method. In epidemiology, where variable conditions are the rule, the repeated observation of associations between covariates by different investigative teams, in different populations, using different designs and methods is typically taken as evidence that the association is not an artifact, [1] for two principal reasons. First, repeated observation adds quantitative evidence that the association is not due to chance alone; second, replication across different designs and populations provides qualitative evidence that the association is not due to uncontrolled bias affecting a single study. Moreover, accumulated evidence can provide more accurate estimates of the effect measures of the risk factor being studied and their uncertainty.
