Frequency Distribution

frequency distribution

In statistics, a graph or data set organized to show the frequency of occurrence of each possible outcome of a repeatable event observed many times. Simple examples are election returns and test scores listed by percentile. A frequency distribution can be graphed as a histogram or pie chart. For large data sets, the stepped graph of a histogram is often approximated by the smooth curve of a distribution function (called a density function when normalized so that the area under the curve is 1). The famed bell curve or normal distribution is the graph of one such function. Frequency distributions are particularly useful in summarizing large data sets and assigning probabilities.

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frequency distribution [¦frē·kwən·sē ‚dis·trə′byü·shən]

(mathematics)

A function which measures the relative frequency or probability that a variable can take on a set of values.

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Frequency Distribution 

a set of the various numerical values of some quantitative characteristic of the members of a population where an indication is given of the frequency of each value—that is, the size of the corresponding group of these members is indicated. A frequency distribution expresses the result of the grouping of the members of the population with respect to a single quantitative characteristic. If the values are ordered, that is, arranged according to increasing or decreasing magnitude, then the frequency distribution is said to be ranked.

A distinction is made between discrete and interval frequency distributions. A discrete frequency distribution is based on a discontinuously varying grouping characteristic; an example is the distribution of workers with respect to the number of machine tools operated. An interval, or grouped (that is, reduced to groups), frequency distribution is based on a continuously varying characteristic; an example of this type is the distribution of a group of people with respect to age. Frequency distributions can also be grouped in the case of a discrete characteristic if the range of this characteristic is sufficiently great—for example, the distribution of urban communities with respect to the number of residents.

The intervals of the grouping characteristic may be equal or unequal. If unequal, they usually increase progressively; this case arises when qualitatively different types of phenomena are being singled out. The sizes of the groups formed are indicated in the frequency distribution by absolute numbers, or frequencies; by relative numbers, or relative frequencies, which are usually percentages of the total; or by both, in two parallel columns. The ratios of the frequencies or relative frequencies to the sizes of the corresponding intervals are called the distribution density.

The importance of frequency distributions in statistics is great. A well-constructed frequency distribution makes possible a detailed analysis of the structure of the population with respect to a given characteristic. Thus, the groups into which the population breaks down can be determined. In addition, the nature of the distribution of the members of the population with respect to the given characteristic can be ascertained—for example, whether the distribution is symmetric or asymmetric or what the degree of concentration of the members is. Finally, various statistics can be calculated, such as the range of the characteristic (the absolute difference between the maximum and the minimum value), the average value of the characteristic, the deviations from the average value, the degree of skewness of the frequency distribution, and the measure of kurtosis (the degree of closeness of a cluster of values of the characteristic around the average value). For easy comprehension, a frequency distribution can be represented graphically in a rectangular coordinate system in the form of a frequency polygon, histogram, cumulative frequency polygon, or ogive. Various combinations of frequency distributions for a population can be presented in the form of statistical tables.

I. G. VENETSKII