Coherence and Focused Hypotheses

Abstract

The 1964 US Surgeon General’s report, Smoking and Health (Bayne-Jones et al. 1964, p. 20), lists five criteria for judgment about causality, the fifth being “the coherence of the association.” A single sentence defines coherence (Bayne-Jones et al. 1964, p. 185): “A final criterion for the appraisal of causal significance of an association is its coherence with known facts in the natural history and biology of the disease.” There follows a long discussion of the many ways in which the association between smoking and lung cancer is coherent. Per capita consumption of cigarettes had, at that time, been increasing, and the incidence of lung cancer was also increasing. Men, at that time, smoked much more than women and had a much higher incidence of lung cancer. And so on. To this, Sir Austin Bradford Hill (1965, p. 10) adds: “ ... I regard as greatly contributing to coherence the histopathological evidence from the bronchial epithelium of smokers and the isolation from cigarette smoke of factors carcinogenic for the skin of laboratory animals.” The pattern of associations in §1.2 between smoking and cardiovascular disease would also be described as coherent. Coherence is discussed by Susser (1973, pp. 154–162) and more critically by Rothman (1986, p. 19). MacMahon and Pugh 1970, p. 21) use the phrase “consonance with existing knowledge” in place of coherence. Coherence is related to Fisher’s “elaborate theory,” as discussed in §1.2.