Oral epidemiology
Prevalence, incidence and disease distribution describe burden. Understand how measurement and sampling affect interpretation.
Understand
Prevalence is the proportion with disease at a point or period; incidence concerns new cases over time. The case definition and sampling frame affect every estimate.
Assess
Check age, geography, deprivation, response rate and diagnostic criteria before comparing surveys. A change in detection method can look like a change in disease.
Apply
Use population data to identify needs and evaluate services, but avoid applying a group average uncritically to an individual patient.
Key distinctions
Cross-sectional prevalence surveys answer different questions from longitudinal incidence studies. Examiner calibration, case definition and response bias can shift estimates. Standardising age and socioeconomic composition may be necessary before comparing regions. Population patterns inform service planning and hypothesis generation but should not be mistaken for the probability of disease in a particular patient.
Think through a case
A survey reports “20% caries prevalence” without age or diagnostic threshold. The figure cannot be compared sensibly with another survey until the methods are clear.
The distinction to remember
Do not use incidence and prevalence interchangeably or infer individual risk directly from a population mean.
Test your recall
What is the difference between incidence and prevalence?
Show answer
Incidence counts new cases over time; prevalence counts existing cases at a point or period.