In a study where data are collected at multiple time points from the same subjects, this design is called:

In a study where data are collected at multiple time points from the same subjects, this design is called:

• A. Longitudinal
• B. Cross-sectional
• C. Prospective
• D. Retrospective

Answer: (A)

Collecting data from the same individuals at multiple time points defines a longitudinal design. This approach tracks how each person changes over time, allowing you to observe trajectories, onset, progression, or responses within individuals rather than comparing different people at a single moment. If you only collect data once from each subject, you’d have a cross-sectional snapshot, which can’t reveal how things evolve. The terms prospective and retrospective describe when data are gathered relative to the study start, and longitudinal studies can be either forward-looking or use existing records, but the defining feature is repeated measurements on the same subjects. So, measuring the same group repeatedly over time best fits the longitudinal approach.

Collecting data from the same individuals at multiple time points defines a longitudinal design. This approach tracks how each person changes over time, allowing you to observe trajectories, onset, progression, or responses within individuals rather than comparing different people at a single moment. If you only collect data once from each subject, you’d have a cross-sectional snapshot, which can’t reveal how things evolve. The terms prospective and retrospective describe when data are gathered relative to the study start, and longitudinal studies can be either forward-looking or use existing records, but the defining feature is repeated measurements on the same subjects. So, measuring the same group repeatedly over time best fits the longitudinal approach.