equal class interval

This is the name given to data which derives from calculations and observations. The data is grouped in classes of the same range. The classes don’t overlap.

For example, the table shows pupils’ marks in a geography examination.

We can see that the class interval is equal as the data has been grouped in tens:

• Mark of 30 up to, but not including, 40

• Mark of 40 up to, but not including, 50

• Mark of 50 up to, but not including, 60

• Mark of 60 up to, but not including, 70

• Mark of 70 up to, but not including, 80

• Mark of 80 up to, but not including, 90.

The equal class interval is 10.