Cumulative Frequency Distribution

Cumulative frequency is obtained by adding the frequency of a class interval and the frequencies of the preceding intervals upto that class interval. This is explained by an example below.

The following frequency distribution table gives the marks obtained by 40 students:

Table (a)

The frequencies can be added, as indicated by the arrows, to obtain the cumulative frequency.

In the table(a), it is observed that 4 students got marks 'less than 10', 9 students got marks 'less than 20' and so on.

Therefore, the above distribution is called 'less than' cumulative frequency distribution.

Table (a) can be re-written as table (b).

Table (b)

In the same way 'more than' cumulative frequency distribution can be obtained by adding to the other frequencies in the reverse order.

Table (c)

The frequencies can be added, as indicated by the arrows, to obtain the cumulative frequency.

Table (c) can be re-written as table (d)

Table (d)