American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Which type of observational study starts with patients who already have a certain outcome?

1. Case series study

2. Cohort study

3. Case report study

4. Cross-sectional study

The correct answer is: Cross-sectional study

The type of observational study that begins with patients who already have a certain outcome is the cross-sectional study. In a cross-sectional study, researchers observe a specific population at a single point in time to assess the prevalence of an outcome or characteristics within that group. This design allows investigators to identify relationships between exposure and outcome but without establishing causality due to its simultaneous measurement. In this context, patients are selected based on the presence of an outcome (e.g., a disease), and their previous exposures or characteristics are evaluated. This is distinct from other types of studies, such as cohort studies, which follow patients over time from an exposure status to see if an outcome occurs, thereby starting without knowledge of the final outcome. Case series and case reports focus on individual cases or small groups rather than a broader population at a specific time, limiting their generalizability.