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Causal Criteria Strength. Hill argued that strong associations are more likely to be causal than weak associations because, if they could be explained by some other factor, the effect of that factor would have to be even stronger than the observed association and therefore would have become evident. Consistency. Consistency refers to the repeated observation of an association in different populations under different circumstances.
Specificity. The criterion of specificity requires that a cause lead to a single effect, not multiple effects. Temporality. Temporality refers to the necessity that the cause precede the effect in time. Biologic gradient. Biologic gradient refers to the presence of a monotonic (unidirectional) dose-response curve.
Plausibility. Plausibility refers to the biologic plausibility of the hypothesis, an important concern but one that is far from objective or absolute. Coherence. Taken from the U.S. Surgeon General's Smoking and Health (1964), the term coherence implies that a cause-and-effect interpretation for an association does not conflict with what is known of the natural history and biology of the disease.
Experimental evidence. It is not clear what Hill meant by experimental evidence. It might have referred to evidence from laboratory experiments on animals or to evidence from human experiments. Analogy. Whatever insight might be derived from analogy is handicapped by the inventive imagination of scientists who can find analogies everywhere.
Abstract Objectives To determine whether starvation during periods of increased growth after birth have long term health consequences. Design Analysis of cardiovascular risk factors and mortality in a longitudinal follow up after the 1941-4 siege of Leningrad. Mortality measured from 1975 up to the end of 1999. Setting St Petersburg, Russia (formerly Leningrad). Participants 5000 men born 1916-35 who lived in Leningrad, randomly selected to take part in health examinations in 1975-7. Of the 3905 men who participated, a third had experienced the siege. Main outcome measures Relative risk of ischaemic heart disease and mortality from stroke by siege exposure. Odds ratios and means for several cardiovascular risk factors.
Results Three to six decades after the siege, in men who experienced the siege around the age of puberty blood pressure was raised (mean difference in systolic 3.3 mm Hg, in diastolic 1.3 mm Hg) as was mortality from ischaemic heart disease (relative risk 1.39, 95% confidence interval 1.07 to 1.79) and stroke (1.67, 1.15 to 2.43), including haemorrhagic stroke (1.71, 0.90 to 3.22). The effect on mortality was partly mediated via blood pressure but not by any other measured biological, behavioural, or social factor. Conclusions Starvation, or accompanying chronic stress, particularly at the onset of or during puberty, may increase vulnerability to later cardiovascular disease.
Random error Systematic error Selection bias BIAS Information bias Confounding Errors in epidemiological inference Error PRECISION: defined as relative lack of random error VALIDITY: defined as relative absence of bias or systematic error “Bias is any process at any stage of inference which tends to produce results or conclusions that differ systematically from the truth” – Sackett (1979) “Bias is systematic deviation of results or inferences from truth.” [Porta, 2008]
COUNTERFACTUAL A conditional statement containing (what looks like) a factually false antecedent. Example: "If I had been in charge, that disaster would have been averted." Strictly speaking, the "antecedent" of this subjunctive is not such because 'I had been in charge' is a phrase, not a sentence designating a proposition. Hence, it cannot be tested for truth anymore than 'a sweet smell'. Therefore it can be neither true nor false. Counterfactual sentences are therefore the stuff of fiction. By contrast, counterfactual questions can be heuristically valuable. In fact, some research projects are sparked off by counterfactual questions such as "What would happen (or would have happened) if A, which is a B, were (or had been) a C?" For example, the economic historian R. W. Fogel asked "How would the modem United States have fared without railways?" He came up with the astounding if controversial answer that the country would have attained roughly the same level of development had alternative means of transportation been used. Bunge 1999
