2.2.1 Concepts involved in frequency tables

The following terms are frequently used in frequency distribution:

Class interval or class limit: The lowest and the highest value defined for a class or group are called class limits. The lowest value is called the lower class limit and the highest value is called the upper class limit of that class. In the example below (see Table 5), the lower class limits are 7, 9, 11, 13, 15, and the upper limits are 8, 10, 12, 14 and 16.

Midpoint or class mark: This is the average of a class interval, and is obtained by dividing the sum of upper and lower class limits by 2. Thus, the class mark of the interval 7– 8 is 7.5, as

Range: this is the difference between the maximum value and the minimum value of the data set. For example, the data set of a student’s score in a maths quiz contains the maximum value 30 and the minimum value 8. Hence, to calculate the range, you must calculate . In the JC Electrics, Generators example, the range is the difference between 15 (as the maximum value sold) and 7 (as the minimum value sold), hence the range is 8.