DANGERS AND ADVANTAGES OF POST HOC ANALYSIS: Post hoc analysis is of major importance in the generation of hypotheses. However, the hypothesis is created by the analysis and has not been proved by any "experiment'. In some circumstances the conclusion derived from a post hoc analysis is entirely appropriate. For example, it was the only method used by Crick and Watson for determining the structure of DNA. In other circumstances, however, the results will be misleading. NEED FOR CAUTION WITH INTERPRETATION: The results of a post hoc analysis should be viewed with considerable scepticism and, in advance of confirmation by other appropriately designed prospective studies, should not be regarded as definitive proof.