Cumulative Distribution

A cumulative frequency distribution is a plot of the number of observations falling in or below an interval. The graph shown here is a cumulative frequency distribution of the scores on a statistics test.

Thirty-eight students took the test. The X-axis shows various intervals of scores (the interval labeled 35 includes any score from 32.5 to 37.5). The Y-axis shows the number of students scoring in the interval or below the interval.

A cumulative frequency distribution can show either the actual frequencies at or below each interval (as shown here) or the percentage of the scores at or below each interval. The plot can be a histogram as shown here or a polygon.