Grouped Data

We can divide data into groups. Such a presentation is called grouped data. The groups are known as classes or class intervals.
The above data can be presented as follows in the from of grouped data.

 Heights (cms) Class intervals Frequency 156 - 160 4 161 - 165 9 166 - 170 6 171 - 175 5 176 - 180 1

We have grouped the data in various class intervals. These class intervals are non-over lapping.

The class 156-160 means that the height of employees lies between 156 cm and 160 cms. (including 156 and 160).

The number of observations falling in a particular class is known as the frequency of that class.

Thus the frequency of class 156 - 160 is 4 and the class 161 - 165 has 9 as class frequency and so on.

156 is called the lower limit of class 156 - 160 and 160 is called upper limit of the class.
The class intervals 156 - 160 is called first class interval. Class interval 161 - 165 is called second class interval. Class interval 176 - 180 is called fifth class interval.
This type of presentation of data is called grouped frequency distribution.