Bradford Hill criteria

Bradford Hill criteria#

The Bradford Hill criteria, established in 1965 by Sir Austin Bradford Hill, are nine principles used to evaluate whether an observed association between a presumed cause and an effect is likely to be causal[1][3]. These criteria have become fundamental in epidemiological research and public health investigations.

The Nine Criteria#

1. Strength of Association The stronger the relationship between a factor and outcome, the more likely it is to be causal[1][4].

2. Consistency The same findings should be observed across different populations, study designs, and times[1].

3. Specificity There should be a one-to-one relationship between cause and outcome[1].

4. Temporality The exposure must precede the outcome - this is a crucial criterion for causation[1].

5. Biological Gradient There should be a dose-response relationship, where changes in disease rates correspond to changes in exposure[1].

6. Plausibility A potential biological mechanism should exist to explain the relationship[1].

7. Coherence The cause-and-effect interpretation should align with existing knowledge[1].

8. Experimental Evidence Experimental studies support the causal relationship[2].

9. Analogy Similar factors may cause similar effects[2].

Modern Application#

These criteria are not meant to be rigid rules but rather “viewpoints” to guide causal inference[4]. Not all criteria need to be satisfied to establish causation[2]. The criteria have proven particularly valuable in public health research, notably in establishing the causal link between smoking and lung cancer[2][4].

Important Considerations#

The criteria must be applied with scientific common sense rather than as a strict checklist[3]. They have evolved with modern science, particularly as our understanding of genetics, molecular biology, and disease mechanisms has advanced[4]. While some debate their current relevance, they remain a fundamental framework for evaluating causal relationships in epidemiology[3].