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A-H represents rating categories according to Newcastle-Ottawa Scale for assessing quality of non-randomized studies
A, Representativeness of the exposed cohort; B, Selection of the non-exposed cohort; C, Ascertainment of exposure; D, Outcome of interest was not present at start of study; E, Comparability of cohorts F, Assessment of outcome; G, Follow-up long enough for outcome to occur? H, Adequacy of follow-up of cohorts.
