Community Health and Research
Community Health and Research
This domain tests population-level measurement, study design, screening, and program planning. You must distinguish clinical care from public health and interpret basic epidemiology correctly.
Core rules
- Prevalence = existing cases at a point in time; incidence = new cases over a period. Prevalence is influenced by incidence and duration.
- DMFT and dmft count decayed, missing, and filled teeth; they are indices, not rates.
- Sensitivity = true positives detected; specificity = true negatives detected. Positive predictive value depends on prevalence.
- Study designs: cross-sectional (prevalence), cohort (incidence and risk), case-control (odds), randomized trial (causality). Bias, confounding, and sampling matter.
- Community programs use screening, education, fluoride, sealants, and referral; screening is not diagnosis.
Worked example
A school of 500 children has 100 with untreated caries at the start of the year; 40 new cases develop by year-end. Prevalence at baseline = 100/500 = 20%. Incidence = 40/(500−100) = 10% among those at risk. Reasoning: baseline cases are excluded from the incidence denominator because they were not at risk of becoming a new case.
Traps
- Reporting DMFT as a percentage rate.
- Using prevalence to infer risk without incidence.
- Assuming high sensitivity means high positive predictive value in a low-prevalence population.
- Calling a screening “diagnosis.”
- Ignoring cultural, language, and access barriers in program design.