How is the study population typically defined in cohort research?

• A. Random Sampling
• B. Only Age Criteria
• C. Inclusion And Exclusion Criteria
• D. Randomized Assignment

Answer: (C)

Defining the study population in cohort research relies on inclusion and exclusion criteria. These criteria specify who is eligible to join the study and who must be left out, shaping the cohort’s characteristics to match the research question and minimize bias. Inclusion criteria set the baseline features participants must have (such as age range, health status, or exposure history), while exclusion criteria rule out individuals whose conditions or factors could confound results or hinder follow-up. Together, they create a well-defined group for observation over time.

Random sampling describes a method for selecting participants from a larger population, but it doesn’t define who qualifies to be in the cohort beyond the sampling frame. Randomized assignment is used in experimental studies to allocate exposures, not to establish a study population in an observational cohort. Relying on age criteria alone is usually insufficient, as many other characteristics influence outcomes and study aims.