Glossary term
Class Interval: Meaning and Definition
Reviewed and approved by Dr. Anamika ShrivastavaPublished Last updated
A class interval is the width of a class in a frequency distribution, found by subtracting the lower limit from the upper limit. Classes are usually kept of equal width so that frequencies can be compared directly. The mid-point of the interval is called the class mark.
In more detail
Equal class intervals make frequencies directly comparable. With unequal intervals, a histogram must use frequency density, or wide classes would look misleadingly tall. The interval is chosen by dividing the range by the planned number of classes, then rounding to a convenient figure.
Example
For the class 40–50 the class interval is 50 − 40 = 10, and the class mark is (40 + 50) ÷ 2 = 45.
Key points
- Class interval = upper limit − lower limit.
- Equal widths allow direct comparison.
- Unequal widths need frequency density in a histogram.
Common mistake
Using inclusive limits to find the interval. Use the true boundaries.
Related terms
Where it is explained
This term is explained in Class 11 Statistics Chapter 3: Organisation of Data.