For example, if the numerator represents new cases of cancer of the ovaries, the denominator should be restricted to women, because men do not have ovaries. The denominator should be limited to the “population at risk” for developing disease, i.e., persons who have the potential to get the disease and be included in the numerator. ![]() The denominator of an incidence proportion is the number of persons at the start of the observation period. Because all of the persons with new cases of disease (numerator) are also represented in the denominator, a risk is also a proportion. The denominator is the number of persons in the population at the start of the observation period. As a measure of incidence, it includes only new cases of disease in the numerator. Incidence proportion is a measure of the risk of disease or the probability of developing the disease during the specified period.Risk = “Food-specific attack rate” = (30 ⁄ 99) × 100 = 0.303 × 100 = 30.3% Properties and uses of incidence proportions Numerator = 30 persons who ate potato salad and developed gastroenteritisĭenominator = 99 persons who ate potato salad Calculate the risk of illness among persons who ate potato salad. ![]() Numerator = 100 deaths among the diabetic menĮxample B: In an outbreak of gastroenteritis among attendees of a corporate picnic, 99 persons ate potato salad, 30 of whom developed gastroenteritis. Calculate the risk of death for these men. EXAMPLES: Calculating Incidence Proportion (Risk)Įxample A: In the study of diabetics, 100 of the 189 diabetic men died during the 13-year follow-up period.
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