Final answer:
Case flow refers to the accumulation of subjects into cases and controls in case-control studies, or cohorts in cohort studies, to analyze and compare data regarding disease states or conditions over time.
Step-by-step explanation:
Case flow refers to the process through which subjects are accumulated into two kinds of groups: those having a trait of interest (cases) and those not having the trait (controls). This method is commonly used in case-control studies, an observational study style where subjects' past behaviors or statuses are compared to determine correlations with current conditions. Another method wherein subjects are grouped is the cohort study, where a similar group of subjects (the cohort) is selected and followed over time in a prospective manner. Cohort studies aim to establish a clear understanding of the potential progression into disease states or conditions of interest. In both types of studies, the accumulation and analysis of subjects are crucial for deriving meaningful results.