Population Health and Health Maintenance
Core concepts
Population health asks you to think beyond the individual: screening principles, prevention levels, and health equity. Know primary (prevent disease), secondary (early detection), and tertiary (limit disability) prevention, and be able to classify an intervention correctly. Screening tests must meet Wilson-Jungner-style criteria: important condition, accepted treatment, early detection benefit, acceptable test, and cost-effective.
Epidemiology basics are testable: sensitivity (rules out when negative - SnNout), specificity (rules in when positive - SpPin), positive/negative predictive values (which depend on prevalence), and number needed to treat. Understand lead-time bias, length-time bias, and selection bias when interpreting screening studies.
Health maintenance means tracking age- and risk-appropriate services: immunizations, cancer screening, and counseling. Population-level interventions include vaccination policy, tobacco taxation, and screening programs. Social determinants (housing, food insecurity, transportation, education) shape outcomes and should be screened for and addressed.
Traps
- Confusing sensitivity and specificity in a stem.
- Ignoring prevalence when interpreting a PPV.
- Misclassifying a prevention level (e.g., calling mammography primary prevention).
- Missing lead-time bias as an explanation for improved survival without mortality benefit.
Rule of thumb
For test interpretation, remember SnNout (high sensitivity, negative test rules out) and SpPin (high specificity, positive test rules in). For prevention-level questions, ask: does this prevent the disease (primary), detect it early (secondary), or reduce its consequences (tertiary)?