What is the difference between a cross-sectional and a cohort study?

What is the difference between a cross-sectional and a cohort study?

• A. A cross-sectional study follows individuals over time to observe outcomes; a cohort study measures exposure and outcome at a single point.
• B. A cross-sectional uses historical records only; a cohort study is randomized.
• C. A cross-sectional assesses exposure and outcome at one point in time; a cohort follows individuals over time to observe incidence and outcomes.
• D. A cross-sectional is experimental; a cohort is qualitative.

Answer: (C)

Time and follow-up define these designs. A cross-sectional study takes a snapshot: exposure and outcome are measured at one point in time, giving a picture of prevalence and associations but not telling which came first. A cohort study starts with groups defined by exposure and follows them over time to see who develops the outcome, yielding incidence data and allowing assessment of temporality and risk. So the correct description is that exposure and outcome are assessed at one time in a cross-sectional, whereas a cohort follows individuals over time to observe incidence and outcomes. The other options misstate temporality, study purpose, or design features (for example, cross-sectional is not limited to historical records, and cohort studies are not randomized).

Time and follow-up define these designs. A cross-sectional study takes a snapshot: exposure and outcome are measured at one point in time, giving a picture of prevalence and associations but not telling which came first. A cohort study starts with groups defined by exposure and follows them over time to see who develops the outcome, yielding incidence data and allowing assessment of temporality and risk. So the correct description is that exposure and outcome are assessed at one time in a cross-sectional, whereas a cohort follows individuals over time to observe incidence and outcomes. The other options misstate temporality, study purpose, or design features (for example, cross-sectional is not limited to historical records, and cohort studies are not randomized).