s fairly simple. First, it is necessary to determine the number of classes that will be used to group the data. Second, the data must be sorted into these classes. Third, the number of items in each class must be counted. The final step in creating a frequency distribution involves displaying the results in either a chart or a table.
The print media commonly make use of frequency distributions. Newspaper and magazine articles often include both charts and tables. Just one example occurred in a recent issue of Airplane Owner's and Pilot's Association (AOPA) magazine. The chart illustrated the results of a recent "learn-to-fly" effort. Participation was subdivided according to month along the chart's horizontal access. From March 1994 to March 1995, the number of students and mentors in the program increased steadily from roughly to 4,000 to approximately 18,000. Unfortunately, while frequency distributions present data in a relatively compact form, there are usually some types of information that can only be obtained from the original data. Thus, although frequency distributions provide data that is more usable, they do so at a price. While information must be lost, the data is ultimately provided with increased comprehensibility.
Most any kind of data contains values which are not all alike. Very often, the degree to which values are unalike is of considerable significance. Therefore, statisticians frequently attempt to define data's variability, or dispersion. Perhaps the simplest and crudest measure of dispersion consists of range. The range of given set of data is simply the difference between its highest and lowest values.
Range is both easy to calculate and easy to understand. Moreover, people have a tendency to focus their attention on highest and lowest values. However, while the range of a given set of data may be interesting, it is not generally a useful measure of variability. This is prima...