graph, they provide a rapid visual comparison without any need to compare
individual intervals. Figure 2.7 gives such a comparison of family incomes
using data of Example 2.5.
The cumulative frequency graph provides a class of important statistics
known aspercentilesorpercentile scores. The 90th percentile, for example,
is the numerical value that exceeds 90% of the values in the data set and is
exceeded by only 10% of them. Or, as another example, the 80th percentile is
that numerical value that exceeds 80% of the values contained in the data set
and is exceeded by 20% of them, and so on. The 50th percentile is commonly
Figure 2.6 Cumulative distribution of weights of 57 children.Figure 2.7 Distributions of family income for the United States in 1983.68 DESCRIPTIVE METHODS FOR CONTINUOUS DATA