On the use of causal criteria.

BACKGROUND: Two recent accounts of the use of causal criteria make opposite claims: that criteria should be used more often to avoid bias in assessments of weak associations and, in direct contrast, that criteria are scientifically invalid.
METHODS: A recent review of the current practice of causal inference in epidemiology, as well as some more theoretical concerns, reveals errors in the two claims.
RESULTS: In practice, epidemiologists often use the criteria of consistency, strength, dose-response, and biological plausibility, but not often temporality, when judging weak associations. These criteria are used for causal assessments as well as for making public health recommendations. In theory, causal criteria can be used to either refute or predict causal effects.
CONCLUSION: Research on causal inference methodology should be encouraged, including research on underlying theory, methodology, and additional systematic descriptions of how causal inference is practised. Specific research questions include: to what extent can consensus be achieved on definitions and accompanying rules of inference for criteria, the relationship of meta-analysis to the criterion of consistency, and the interrelationships of criteria such as consistency, strength of association, and biological plausibility.