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How do cohort studies follow exposed and unexposed groups over time?

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Know the investigations of researchers using genomic information to reconstruct the cause and transmission routes of the bubonic plague and the Black Death — epidemiology Researchers using genomic information to trace the transmission routes in past epidemics of plague.

In epidemiology, a cohort study is an observational research design that tracks a defined group of people, known as a cohort, over a period of time to compare health outcomes between individuals based on their exposure status to a specific factor.1

Researchers follow these groups using two primary approaches:

Concurrent cohort studies: The cohort is assembled in the present and monitored as they move forward into the future.1
Historical cohort studies: The cohort is identified by reviewing past records, allowing researchers to analyze outcomes that have already occurred over a specific timeframe.1

By observing these groups, investigators can determine the timing and directionality of events, helping to establish whether statistical associations exist between suspected causal factors and the occurrence of disease. While these studies are powerful for identifying such links, they require large sample sizes and long follow-up periods, making them less suitable for investigating rare diseases compared to case-control studies.1