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Abstract

Bradford Hill's considerations published in 1965 had an enormous influence on attempts to separate causal from noncausal explanations of observed associations. These considerations were often applied as a checklist of criteria although they were by no means intended to be used in this way by Hill himself. Hill, however, avoided defining explicitely what he meant by "causal effect". This paper provides a fresh point of view on Hill's considerations from the perspective of counterfactual causality. I argue that counterfactual arguments strongly contribute to the question when to apply them. Some considerations, however, involve many counterfactuals in a broader causal system and their heuristic value decreases with increasing complexity of a system; the danger of misapplying can be high. The impacts of these insights for study design and data analysis are discussed. The key analysis tool to assess the applicability of Hill's considerations is multiple bias modelling (Bayesian methods and Monte Carlo sensitivity analysis); these methods should be used much more frequently.