Britannica Sources used in this answer

Why are cohort studies not well suited to investigating rare diseases?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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, cohort studies are generally not well suited for investigating rare diseases because they require very large sample sizes and long follow-up periods to ensure that a sufficient number of cases emerge to provide statistically significant results.1

Because cohort studies involve following a defined group of people over time to observe the development of an outcome, they are inefficient when the disease of interest occurs infrequently in the population. In such cases, researchers would need to monitor an impractically large number of individuals for an extended duration to capture enough events for analysis.1

In contrast, case-control studies are considered the most practical option for rare diseases. By starting with individuals who already have the disease (cases) and comparing them to a control group, these studies bypass the need to wait for new cases to emerge, thereby requiring fewer resources and smaller sample sizes.21