Which is the preferred statistic for risk, incidence or prevalence?

• A. Prevalence
• B. Attack rate
• C. Incidence
• D. Incidence density

Answer: (C)

Risk is about the chance of developing a disease over a defined period, so the best summary is incidence, specifically cumulative incidence, which is the number of new cases divided by the population at risk at the start of the period. This yields a probability-like measure of developing disease during that time.

Prevalence accounts for everyone with the disease at a given moment or over a period, including long-standing cases, so it reflects how widespread the disease is rather than the risk of acquiring it. Attack rate is a related concept used in outbreaks to estimate risk within a defined group over a short interval, but the general measure of risk in a population over time is incidence. Incidence density uses person-time and provides a rate; it’s more precise when follow-up times vary, but it isn’t a direct probability of developing disease, which is what risk represents.