Analytic epidemiologic methods for research on nosocomial infections: definitions and examples.
Two types of epidemiologic studies are presented: the cohort study and the case-control study. The fundamentals distinction between the two methods is in the definition of the population groups for study. The cohort approach identifies groups with different exposure histories, whereas the case-control approach begins with groups with different health and disease characteristics. The investigation in the cohort method involves collection of data on the disease experience of the various exposure groups from date of exposure to some later follow-up date. Data collection in the case-control study is concerned with the exposure history prior to the date of the identified health and disease status. Both approaches are satisfactory in general, but either may have distinct advantages in a given study, depending chiefly on the frequencies of exposure and disease and on the nature of biases inherent in available data.
D003428:Cross Infection / Q000453:epidemiology*; D003625:Data Collection / Q000379:methods; D004812:Epidemiologic Methods; D006801:Humans; D011336:Probability; D012306:Risk