Public Health, Epidemiology and Health Promotion
Public Health, Epidemiology and Health Promotion tests population health measurement, prevention and national programmes. In Cambodia, questions may link pharmacy practice to immunisation, tuberculosis, malaria, dengue, HIV and maternal-child health programmes.
Core rules
- Incidence measures new cases over time; prevalence measures existing cases at a point or period. Prevalence rises with longer duration and falls with cure or death.
- Sensitivity detects true cases; specificity detects true non-cases. Positive predictive value depends on prevalence as well as test accuracy.
- Prevention levels: primary prevents onset; secondary detects early; tertiary reduces complications and disability.
- Health promotion uses education, policy, community participation and enabling environments, not only individual advice.
Worked example
A screening test has 90% sensitivity and 95% specificity in a population with 1% prevalence. PPV = (0.90 × 0.01)/[(0.90 × 0.01) + (0.05 × 0.99)] = 0.009/0.0585 = 15.4%. Even with good test accuracy, most positives are false positives when prevalence is low; confirmatory testing is essential.
Traps
- Confusing sensitivity with PPV.
- Ignoring prevalence when interpreting a screening result.
- Calling a longer survival time “better” when it reflects earlier diagnosis (lead-time bias).
- Treating health education as the same as health promotion.