47, 58, 94, 87, 60, 75, 34, 27, 82, 63, 56, 50, 59, 40, 28, 12, 18, 77, 69, 10.
In the above data, no classification is made and hence it is a raw data.
- Grouped data
Data represented in various groups or classes is called grouped data.
Eg. : Consider the data in item 6. The data can be classified as follows:
- Class interval
After the collection of the numerical data they are classified into suitable groups as
per the convenience. The groupings with a lower limit and a upper limit are called as
the class intervals. The size of the class intervals should be equal in size. The size of
a class interval is also called as class width. The middle value of the class interval is
called the class mark.
Eg. : In the above example, all class intervals 1-20, 21-40, 41-60, etc., are of equal size.
- Frequency
The number of observations which fall in one particular class interval is called the
frequency of the class interval. To determine the frequency of each class interval tally
marks are made for each datum in that class till all the data are exhausted.
Eg. : In the example in item 7, the frequency of the class interval 41-60 is 6.
- Frequency distribution table
Grouped data presented in a table form listing class intervals and corresponding
frequencies is called a frequency table.
C-I Frequency
1-20 3
21-40 4
41-60 6
61-80 4
81-100 3
