A strengthening programme for weak associations.

The strength of a causal association depends on the relative prevalence of other component causes for the same disease. Weak associations may sometimes be strengthened by restricting attention to people at low risk. This technique may lead to fewer subjects to study, but nevertheless may provide more information by which to evaluate a causal relation. A second method for strengthening associations is to reduce non-differential misclassification, which tends to dilute associations. Increasing the specificity of measurement for exposure, disease, and the timing between causal action and disease onset should produce stronger associations that are easier to interpret and more descriptive of the underlying causal mechanism.