DEFINITION of 'Frequency Of Exclusion '
Frequency of exclusion refers to the rate of occurrence of a given group being excluded from a sample or study. The frequency of exclusion defines the percentage or rate that a specified group is underrepresented in a sample or study.
BREAKING DOWN 'Frequency Of Exclusion '
Statistics is a type of mathematical study that aims to gather, review and analyze data to draw conclusions about a population, whether that population is a group of things, people, animals or anything else with common characteristics that a statistician seeks to understand. Because the population being studied can be very large, such as the human race or the population of evergreen trees on the planet, collecting and analyzing data on the entire group may be infeasible.
Statisticians instead select a representative subset or sample of the entire population in these cases. A sample is a smaller, more manageable version of the entire population. The determination of samples should ideally be unbiased, but statisticians may leave out given members of the entire population being studied, either intentionally or inadvertently. Frequency of exclusion can be determined for these population members, and can indicate if those members are categorically overlooked in a statistical study.
Why Frequency of Exclusion Matters
Statistical study results lose their meaningfulness if certain members of the population have a high frequency of exclusion from the sample because the results will not accurately represent the entire population of interest. For example, one could determine the rate at which persons with a certain blood type are excluded from a particular medical study on a promising new pharmaceutical drug. If for instance, the study excluded type B positive blood types, the frequency of exclusion for type B positive blood would be 100%, and the study results will not accurately reflect the effects of the tested drug that may occur when taken by the general public, a portion of whom have type B positive blood.
Because an important and relevant member group of the population was excluded from the study, the results lack statistical significance. Conversely, if a statistician excluded a member grouping because it represents a statistically insignificant amount of the entire population, such as excluding the evergreen trees in Hawaii in a study of evergreens on the planet, although the frequency of exclusion is 100% for the group of evergreens in Hawaii, the statistical significance of the study should be unaffected.

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