Percentage Frequency Distribution

A percentage frequency distribution is a display of data that specifies the percentage of observations that exist for each data point or grouping of data points. It is a particularly useful method of expressing the relative frequency of survey responses and other data. Many times, percentage frequency distributions are displayed as tables or as bar graphs or pie charts.

The process of creating a percentage frequency distribution involves first identifying the total number of observations to be represented; then counting the total number of observations within each data point or grouping of data points; and then dividing the number of observations within each data point or grouping of data points by the total number of observations. The sum of all the percentages corresponding to each data point or grouping of data points should be 100%. The final step of creating a percentage frequency distribution involves displaying the data.

For example, as part of a study examining the relationship between number of trips to a physician and socioeconomic status, one might survey 200 individuals about the number of trips each made to a physician over the past 12 months. The survey might ask each individual to choose from the following responses: "0 times during the past year," "1-3 times during the past year," "4-6 times during the past year," "7-9 times during the past year," and " 10 or more times during the past year."

If 10 respondents were to select the first response, 80 were to select the second, 50 were to select the third, 40 were to select the fourth, and 20 were to select the fifth, then the percentage frequency distribution would be calculated by dividing the number of responses for each choice by the total number of responses, or 200. The percentage frequency of each would be 5%, 40%, 25%, 20%, and 10%, respectively. The percentage frequency distribution is shown in table form (Table 1) and in bar graph form (Figure 1).

Alternatively, one could aggregate—or group— data points. For instance, in the previous example, a percentage frequency distribution could group the number of trips to the doctor into three distinct categories, such as "0 times," "1 to 6 times," and "7 or more times." When grouping the responses, the total percentage of each category of response is merely the sum of the percentages for each response. When grouped in this manner, the frequency percentage of "0 times" would remain unchanged at 5%, the total for "1 to 6 times" would be 65% (the sum of 40% and 25%), and the total for "7 or more times" would be 30% (the sum of 20% and 10%).

Figure 1 Percentage frequency distribution

Most statistical software programs can easily generate percentage frequency distributions and provide visual representations in table or graph form.