2.9: Relative Frequency Histogram

The relative frequency depicts the proportion of data points that have each value. The frequency tells the number of data points that have each value. Like the histogram, a relative frequency histogram also has the same shape with a horizontal scale (the x-axis), but the vertical scale (the y-axis) is marked with relative frequencies (percentages of the whole) instead of actual frequencies. A relative frequency histogram is a graphical representation of a frequency distribution where the heights of rectangle bars indicate the frequency with data falling into the associated classes, while the bar's width and position indicate the various classes. Frequency histograms must be labeled with either class midpoints or with class boundaries. The purpose of this graph is to check the distribution of data.

Consider a relative frequency distribution table of the number of clocks sold at different price ranges represented as class intervals and class boundaries. This table represents the relative proportions of each quantitative value in the data set.

Such relative frequency tables are visualized using a graph called relative frequency histograms. Here, the vertical axis represents the relative frequencies of each class, and the horizontal axis represents the class boundaries or the class midpoints. 

Then, the vertical bars of equal width are drawn without gaps, connecting the class boundaries with the relative frequency values. From such histograms, one can understand how often any value occurs relative to the others in the data set.

Suppose the data are expressed in percentage frequencies; they are then visualized using the percentage frequency histogram. Here, the second bin shows that 17 percent of the total clocks sold fall between the price of 10.5 and 16.5 dollars. 

If the data set is too large, plotting them on a histogram makes it easier to interpret.