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Chapter 1: Introduction and Graphical Displays
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Once the number of classes has been decided on, one may compute the class
width. The class width is computed from the minimum and the maximum
values for the data set and the number of classes. The class width is the
difference between two consecutive lower class limits in the distribution.
The class width is computed using the following formula:
Note:
When the class width is computed, one can use common sense to choose
reasonable widths. For instance, if the class width is computed to be 8.5342,
a reasonable class width to use would be 10. This will make things less
complex.
Example 1-3:
The following data represent the amount of money (in
dollars) spent during a month on social activities by a sample of 30 college
students. Summarize the information with a frequency distribution using
seven classes.
Solution:
Using the
Histogram from Raw Data
workbook, a histogram
with seven classes is given in
Figure 1-11
. The computed class width is
8.7142, so a reasonable class width to use is 10. The minimum value is 90
and the maximum value is 151 so a reasonable starting point or bin was 85
with a bin size or class width of 10, and ended at 155. By using these