Question

Prevalence of a disease:

• A. Is the best measure of disease frequency in etiological studies.
• B. Can only be determined by a cohort study.
• C. Is the number of new cases in a defined population.
• D. Describes the balance between incidence, mortality and recovery.

Hint:

Prevalence = incidence x average duration; duration is shortened by death or cure, so prevalence reflects that balance.

Answer 1

The Correct Option is D

This question checks whether we can tell prevalence apart from incidence and know what actually drives the size of a prevalence pool. Let's look at each option.

1. Is the best measure of disease frequency in etiological studies: wrong. For studying causes of disease, incidence is preferred because it tracks new events over time; prevalence blends old survivors with fresh cases and gets distorted by how long people live with the disease.
2. Can only be determined by a cohort study: wrong. Prevalence is most often measured through a simple cross-sectional survey at one time point, not only by following a cohort over years.
3. Is the number of new cases in a defined population: wrong. That is the definition of incidence. Prevalence counts every existing case, whether newly diagnosed or long standing, at the time of the count.
4. Describes the balance between incidence, mortality and recovery: correct. New cases (incidence) add to the prevalence pool, while death and recovery/cure remove cases from it, so the pool size at any moment reflects this constant inflow and outflow.

The only statement that correctly matches how prevalence behaves is the last one.

Let's summarize:

• Incidence counts new cases and suits cause and effect research; prevalence counts all existing cases and suits planning health services.
• Prevalence goes up with more incidence or longer survival with disease, and goes down with faster death or cure.

So the correct description of prevalence is: it describes the balance between incidence, mortality and recovery.