Class interval
Also called: Class width · Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 3 "Organisation of Data"; Class 11, Ch 8 "Use of Statistical Tools"
Meaning
The class interval, also called the class width, is the size of a class. It is the difference between the upper and lower class limits.
Class interval = Upper class limit − Lower class limit
The class width and the range (largest value minus smallest value) together decide how many classes you get: number of classes = range ÷ class width. Usually there are 6 to 15 classes. Class intervals can be unequal when the range is very large, as with incomes, or when values bunch in a small part of the range.
Example
In NCERT's marks table (0-10, 10-20 … 90-100), each class has an interval of 10 − 0 = 10. The range of 100 marks divided by a width of 10 gives 10 classes.
Don't confuse with
- Range: the spread of all the data (largest minus smallest value), not the width of one class.
Related concepts
- Raw data
- Classification
- Chronological classification
- Spatial classification
- Qualitative classification
- Quantitative classification
- Attribute
- Continuous variable
- Discrete variable
- Frequency