Biostatistics & Research · patient case question
A report states the total number of people living with a disease in the year 2000. Which measure is this?
Patient case: Patient who refuses whitening because of a cancer claim
Patient: Female, 38 years old
Chief Complaint: Interested in tooth whitening but has read online that it causes cancer.
Background: She raises the concern at consultation. The clinician wishes to find the best available evidence on whether vital tooth whitening is associated with oral cancer risk, in order to counsel her properly.
Current Findings: No relevant medical history. Generalised extrinsic staining. Sound dentition.
Show answer and explanation
Correct answer: B. Prevalence
- A. Attributable risk is the excess risk in the exposed group attributable to the exposure.
- B. CORRECT. Prevalence is the total number of EXISTING cases — new and old together — present in a population at a given time. It measures the burden of disease and is the figure that matters for planning services and allocating resources.
- C. Incidence counts only NEW cases arising during a defined period. It measures risk of developing the disease and is the figure used to study causation.
- D. Relative risk compares the incidence between an exposed and an unexposed group. It is a ratio, not a count.
Note: The relationship worth remembering: prevalence ≈ incidence × duration. A disease that is common but short-lived has high incidence and low prevalence; a chronic incurable disease accumulates prevalence even with modest incidence.
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