How Do Medical Researchers Make Causal Inferences?

Abstract

Bradford Hill (1965) highlighted nine aspects of the complex evidential situation a medical researcher faces when determining whether a causal relation exists between a disease and various conditions associated with it. These aspects are widely cited in the literature on epidemiological inference as justifying an inference to a causal claim, but the epistemological basis of the Hill aspects is not understood. We offer an explanatory coherentist interpretation, explicated by Thagard's ECHO model of explanatory coherence. The ECHO model captures the complexity of epidemiological inference and provides a tractable model for inferring disease causation. We apply this model to three cases: the inference of a causal connection between the Zika virus and birth defects, the classic inference that smoking causes cancer, and John Snow’s inference about the cause of cholera. Introduction Bradford Hill asked “In what circumstances can we pass from ... [an] observed association to a verdict of causation? Upon what basis should we proceed to do so?’’ (Hill 1965, p. 295) Hill’s expertise lay in the relationship between work conditions and illness. He often 1 Acknowledgments: Thanks to Mike Bishop, Kostos Kampouratis, Kevin McCain, and Chase Wrenn for comments on an earlier draft.