MathGloss/C/Class interval

Examples
Pulse rates, in beats per minute, were calculated for $$192$$ students enrolled in a statistics course at the University of Adelaide. The pulse rates in the dataset range from $$35$$ to $$104$$ beats per minute, $$70$$ possible values. An ungrouped frequency distribution listing the counts for each of the $$70$$ possible values will be large and cumbersome to interpret effectively. Interpretation is simplified by grouping the data into class intervals.

Use the number of observations, in this example $$n=192\,$$, to determine the number of class intervals to use in a grouped frequency distribution:


 * Sturgis's rule, $$1 + 3.3\,log_{10}192=8.6\,$$, suggests $$8$$ or $$9$$ class intervals.


 * The Rice rule, $$2 \times \sqrt[3]{192}=11.54$$, suggests $$11$$ or $$12$$ class intervals.

There is no right answer for the number of class intervals. For this example we will group the data into $$10$$ classes, splitting the difference between the two methods.

The following frequency table provides the count and percent for the data values grouped into $$10$$ class intervals.

"not including", and the square bracket, which means "including".
 * The limits of each class are indicated by the parenthesis, which means