Uses of Prevalence and Incidence Measures:

• Prevalence: administration, planning, some research
• Incidence: etiologic research (problems with prevalence since it combines IR and D), planning
• Similar to incidence, persons included in the denominator must have the potential for being in the numerator, i.e. at-risk for the disease or condition. Prevalence is often expressed after multiplication by 100 (%), 1000 or 100,000.
• The term rate may be inappropriately applied to prevalence. Prevalence is a proportion, usually reflecting the proportion with a disease at a particular time. (point prevalence)
• The prevalence pool is the subset of the population with the condition of interest. The prevalence pool is not generally useful for hypothesis-driven epidemiologic research because these are not new cases, but can be useful in tracking the natural history of the disease, evaluating effects of treatments or disease burden.
• For most etiologic research, incidence is the more appropriate measure. Studying the incidence of a rare condition however, poses a challenge. Given a small number of new cases, it can be preferable to estimate prevalence instead of incidence in these situations. For example, birth defect rates, reported as the numbers of cases/live births is a prevalent measure.Similarly, an autopsy rate is a prevalent measure.
• Two common measures are point prevalence and period prevalence. The difference is whether the estimate is made over a period of time or at one specific time