Organisation of Data — Economics STD 11 Commerce — Question

Cumulative Frequency series is one in which the frequencies are continuously added corresponding to each class interval of the series. It can be prepared from discrete frequency distribution as well as continuous frequency distribution. It can be of two types:

1. Cumulative Frequency Series of less than type: It is prepared on the basis of upper limit and show how many items lie below some value.
2. Cumulative Frequencies of more than type: These are prepared on the basis of lower limit of the classes and shows how many items lie above a given value.

Let us take an example to understand how a simple series is converted into cumulative frequency series.
Suppose we know the marks distribution of 50 students in the form of a simple continuous frequency distribution.

Marks	Frequency
0-10	4
10-20	7
20-30	4
30-40	3
40-50	2

Cumulative frequency series of less than type

Marks	Frequency
Less than 10	4
Less than 20	4 + 7 = 11
Less than 30	11 + 4 = 15
Less than 40	15 + 3 = 18
Less than 50	18 + 2 = 20

Cumulative frequency series of more than type

Marks	Frequency
More than 10	20
More than 20	20 - 4 = 16
More than 30	16-7 = 9
More than 40	9-4 = 5
More than 50	5-3 = 2