External validity, or generalizability, in cohort studies depends on which aspects?

• A. External validity is solely about sample size.
• B. External validity depends on representativeness, setting, and exposure/outcome definitions relative to other populations.
• C. External validity depends only on outcome measurement accuracy.
• D. External validity is irrelevant to cohort studies.

Answer: (B)

External validity, or generalizability, asks whether findings from a cohort study would apply to other populations beyond the study sample. The crucial factors are how representative the study sample is of the target population, the setting in which the study was conducted, and whether the exposure and outcome definitions used in the study match those used in the populations to which you want to generalize. If the sample is not representative, the setting is very different, or the exposures/outcomes are defined differently, applying the results elsewhere becomes questionable.

While large sample size and precise outcome measurement improve the study’s internal validity and precision, they do not by themselves guarantee generalizability. External validity matters for cohort studies because we often want to extend findings beyond the exact group studied.