Details and Examples: PARETO Procedure

Scaling the Cumulative Percent Curve

Pareto charts shown in textbooks typically scale the cumulative percent curve so that it is anchored at the top right corner of the leftmost bar. The upper end of the primary vertical axis is then extended to accommodate the curve. For an illustration, see Output 15.2.1. By default, the PARETO procedure uses the top right corner as the anchor position on a vertical chart and the bottom right corner of the topmost bar as the anchor position on a horizontal chart. You can override the default with the ANCHOR= option.

This method of scaling is not feasible if the number of categories is very large and if the Pareto distribution is uniform. In this case, the bars are excessively compressed relative to the curve. Conversely, this method excessively compresses the curve relative to the bars when you use a count scale for the frequency axis in a comparative Pareto chart and the tallest bar does not occur in the key cell. In either situation, the procedure overrides the textbook scaling method and balances the scales of the bars and the curve.

You can use the AXISFACTOR= option to specify the extent to which the frequency axis should be extended. Alternatively, you can extend the frequency axis by using the VBAR statement VAXIS= option or HBAR statement HAXIS= option to specify the tick mark values for the axis.

Another scaling anomaly is illustrated by the comparative Pareto chart in Output 15.1.4. Here, the cumulative percent curve in the bottom chart is not anchored due to the combination of a uniform count scale and different sample sizes in the two cells.