Critical appraisal of a matched case–control study
This chapter presents a matched case-control study, of historical importance as the first report of an important aetiological relationship which was subsequently confirmed. It shows the methods for a small matched study, and the complexities of separating the effects of a treatment from the effects of indications for the treatment. The critical assessment follows the scheme set out in chapter 10: describing the study, assessing the non-causal explanations of observation bias, confounding, and chance variation; assessing time relationships, strength, dose-response, consistency and specificity, and applying the results to the eligible, source, and target populations; and then comparing the results with evidence from other studies, considering consistency and specificity, biological mechanisms, and coherence with the distribution of exposures and outcomes. The chapter gives a summary and table of the critical assessment and its conclusions; and comments on the impact of the study and research carried out since.