![]() A proportion may be expressed as a decimal, a fraction, or a percentage. You might use a proportion to describe what fraction of clinic patients tested positive for HIV, or what percentage of the population is younger than 25 years of age. It is a type of ratio in which the numerator is included in the denominator. ![]() Proportion Definition of proportionĪ proportion is the comparison of a part to the whole. Therefore, the death-to-case ratio is a ratio, but not a proportion. Thus many of the 802 in the numerator are not among the 15,075 in the denominator. Note that, presumably, many of those who died had initially contracted tuberculosis years earlier. Dividing both numerator and denominator by the denominator (and multiplying by 10 n = 100) yields 5.3 deaths per 100 new cases. Dividing both numerator and denominator by the numerator yields 1 death per 18.8 new cases. The tuberculosis death-to-case ratio for 2002 can be calculated as 802 ⁄ 15,075. It is used as a measure of the severity of illness: the death-to-case ratio for rabies is close to 1 (that is, almost everyone who develops rabies dies from it), whereas the death-to-case ratio for the common cold is close to 0.įor example, in the United States in 2002, a total of 15,075 new cases of tuberculosis were reported.( 3) During the same year, 802 deaths were attributed to tuberculosis. A commonly used epidemiologic ratio: death-to-case ratioĭeath-to-case ratio is the number of deaths attributed to a particular disease during a specified period divided by the number of new cases of that disease identified during the same period. Thus, Delaware’s infant mortality rate was 2.8 times as high as New Hampshire’s infant mortality rate in 2001. Calculate the ratio of the infant mortality rate in Delaware to that in New Hampshire. You could also divide each value by 1.25, and express this ratio as 1 clinic for every 8,000 persons.Įxample B: Delaware’s infant mortality rate in 2001 was 10.7 per 1,000 live births.( 2) New Hampshire’s infant mortality rate in 2001 was 3.8 per 1,000 live births. To get a more easily understood result, you could set 10 n = 104 = 10,000. Calculate the ratio of clinics per person.ĥ00 ⁄ 4,000,000 × 10 n = 0.000125 clinics per person So the ratio of non-diabetics to diabetics cited in the previous example is more likely to be reported as 16.7:1 than 3,151:189.ĮXAMPLES: Calculating Ratios for Different VariablesĮxample A: A city of 4,000,000 persons has 500 clinics. Usually, the values of both the numerator and denominator of a ratio are divided by the value of one or the other so that either the numerator or the denominator equals 1.0.In other words, you are free to use a ratio to compare the number of males in a population with the number of females, or to compare the number of residents in a population with the number of hospitals or dollars spent on over-the-counter medicines. As noted previously, the numerators and denominators of a ratio can be related or unrelated.These ratio measures, including risk ratio (relative risk), rate ratio, and odds ratio, are described later in this lesson. ![]() As an analytic tool, ratios can be calculated for occurrence of illness, injury, or death between two groups. As a descriptive measure, ratios can describe the male-to-female ratio of participants in a study, or the ratio of controls to cases (e.g., two controls per case). In epidemiology, ratios are used as both descriptive measures and as analytic tools.
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