STATS Flashcards
The relationship among incidence (I), prevalence (P), and duration (D) of disease is best expressed as:
Incidence is defined as the number of new cases of a disease in a given period, and prevalence is the number of total cases prevailing (counted) in the given period.
Prevalence can increase (or decrease) in two ways: 1) the number of new cases (incidence) increases (or decreases) and 2) the duration of disease increases (or decreases). If a disease goes untreated, for example, duration would likely increase, (compared to treated cases), and prevalence would increase.
Similarly, if the risk of acquiring a disease increased, the prevalence would increase. Thus, prevalence can generally be viewed as the product of incidence and disease duration. Note, for example, that if the weekly incidence of a disease were 5 new cases and the duration was 2 weeks per case (on average), generally one would expect the weekly prevalence to be 5 cases/week x 2 weeks = 10.
Ref: Giesecke pg. 9, Smith R: pg. 81, Martin, Meek, Willeberg
