Population health and the context of general practice
Population health and the context of general practice
This domain tests screening logic, epidemiology, prevention in practice, and the Australian health system context - Medicare, the Pharmaceutical Benefits Scheme, and equity of access.
Core rules
- Screening criteria (Wilson and Jungner): the condition must be important, have a detectable latent stage, an accepted test, and evidence that early treatment improves outcome. Screening is offered to asymptomatic people; case-finding in a symptomatic patient is ordinary clinical care.
- Test metrics: sensitivity and specificity are properties of the test; positive predictive value depends on prevalence. Lower prevalence means more false positives.
- Prevention in practice: the 5As (assess, advise, agree, assist, arrange); brief intervention for smoking and alcohol; opportunistic immunisation.
- Equity: social determinants, Aboriginal and Torres Strait Islander health assessments, interpreters, and bulk-billing decisions all shape who actually receives care.
- Notifiable diseases: reporting is mandated under state and territory public health legislation, not by the Commonwealth.
Worked example
A screening test has 90% sensitivity and 95% specificity; prevalence is 1%. What is the positive predictive value?
In 1,000 people: 10 have disease, of whom 9 test positive. Of the 990 without disease, 5% (49.5) test positive. PPV = 9 / (9 + 49.5) = about 15%. Reasoning: four in five positive results are false positives, which is why screening positives require confirmatory testing and why counselling before screening matters.
Traps that cost marks
- Assuming a highly specific test rules in disease when prevalence is very low.
- Confusing incidence (new cases per population per time) with prevalence (all existing cases).
- Quoting relative risk reduction without the absolute figure.
- Describing a screening program for a symptomatic presentation.