 Association is the concurrence of two factors more than expected by chance. The following are the considerations used to assess whether an observed association between an exposure and an outcome is likely to be causal. A higher strength of association or effect size between exposure and outcome consistency or reproducibility observed in different studies, populations and circumstances. Specificity exposure is associated with a specific outcome and the outcome is not linked to multiple exposures. Caus must precede the effect in time. Biological gradient or dose response relationship that higher levels of exposure are associated with a higher risk of the outcome. Plausibility and the proposed causal relationship aligns with current biological knowledge that causal relationship is coherent or consistent with other known facts and does not conflict with established principles. Experimental evidence can provide stronger support for causation. Analogy similarities to other established causal relationships. Some epidemiologists prioritize ruling out chance, bias and confounding to derive causation from association over Hill's criteria.