Class interval refers to the numerical width of any class in a particular distribution.
Mathematically it is defined as the difference between the upper class limit and the lower class limit
Class Interval= Upper Class limit – Lower class limit
In statistics, the data is arranged into different classes and the width of such class is called class interval. Class intervals are generally equal in width but this might not be the case always.
Also, they are generally mutually exclusive. Class Intervals are very useful in drawing histograms.
For example the following are the data of ages of a randomly selected population of 10 people
8, 19, 58, 35, 45, 12, 6, 13, 18, 47
Then they are grouped as follows:
60 and above
Here, class interval is 10-0=20-10=30-20= 10
In firs row, upper limit=10, lower limit= 0, class width= 10-0=10.
The grouping can be done differently with different class intervals also.