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| EPI2-1: Measures of Occurrence: Absolute And Relative Measures |
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| EPI2-1: Measures of Occurrence: Absolute And Relative Measures |
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OBJECTIVES |
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At the end of this session you should have an understanding of the importance of being able to express numbers of health events relative to some population as a denominator, so that occurrence of health events can be meaningfully compared between populations. |
Measures of disease occurrence should generally be independent of the size of the population.
To accomplish this, the number of cases of disease is related to the number of individuals in the population generating the cases.
For some administrative purposes the absolute number of cases may be relevant, but for most analytical purposes the size of the population that gives rise to the cases has to be taken into account.
In a campaign aimed to encourage the use of hearing protection devices, some epidemiologic data were provided. Out of 125 workers with noise-induced hearing loss, only 11 used hearing protectors, while 114 did not. These data were presumed to suggest an association between use of hearing protectors and noise-induced hearing loss. The comparison, however, involves two absolute numbers of cases; the sizes of the two populations that gave rise to those with hearing loss, those who wore hearing protectors and those who did not, have not been taken into account. The observed discrepancy might well reflect only that the size of the population of hearing protector users is small compared with the size of the population of nonusers.
