Statistics are best represented graphically using a bar graph forqualitative representation and a frequencyhistogram for quantitative representation. Anexample of a frequency histogram and what it contains is as follows.

When forming a frequency histogram be sure to follow these guidelines. Useintervals of equal length with midpoints at convenient round numbers. For asmall data set use a small number of intervals. For a large data set use moreintervals.

A frequency table is a good summary of data. Divide the number line intointervals to get the class interval. Count the number of data points within eachinterval to get the frequency. The relative frequency is the frequency dividedby the total number of data points, thus the relative frequency can never bemore than one since it represents a part of the whole.

Once the frequency table has been created, the data need to be graphed tocreate the frequency histogram. To do this the midpoint of the interval needsto be plotted on the x (horizontal) axis, and the number in the interval needsto be plotted on the y (vertical) axis. In the example given above, thenumbers of the midpoints of the intervals (95, 110, 125 to 215) would beplotted, then lines would be drawn to the appropriate number do subjects inthat interval (2,9,19 to 1). This would provide us with a visualrepresentation of the number of subjects whose scores fell within the specificinterval.