Which statement contrasts prospective and retrospective studies?

Which statement contrasts prospective and retrospective studies?

• A. Prospective studies plan to collect data forward in time; retrospective studies examine past records
• B. Prospective studies examine past records; retrospective studies collect data forward in time
• C. Prospective studies are always randomized; retrospective studies are never randomized
• D. Prospective studies have no bias; retrospective studies have bias

Answer: (A)

The key idea is how data are collected over time: forward-looking versus backward-looking. Prospective studies plan to collect data going forward in time, starting at enrollment and following participants into the future to observe outcomes. Retrospective studies, in contrast, look back at existing records to determine what happened in the past. This distinction in the temporal direction of data collection is exactly what the statement captures. Other options misstate this contrast or add claims about randomization and bias that aren’t inherent to the prospective vs retrospective distinction. For example, not all prospective studies are randomized (many are observational cohorts), and both designs can have biases—prospective studies can still face loss to follow-up, while retrospective studies can suffer from missing data and information bias.

The key idea is how data are collected over time: forward-looking versus backward-looking. Prospective studies plan to collect data going forward in time, starting at enrollment and following participants into the future to observe outcomes. Retrospective studies, in contrast, look back at existing records to determine what happened in the past. This distinction in the temporal direction of data collection is exactly what the statement captures.

Other options misstate this contrast or add claims about randomization and bias that aren’t inherent to the prospective vs retrospective distinction. For example, not all prospective studies are randomized (many are observational cohorts), and both designs can have biases—prospective studies can still face loss to follow-up, while retrospective studies can suffer from missing data and information bias.