Unformatted text preview: uld be included in the class interval
500010000. This method is widely used in practice.
b) Inclusive method:
In this method, the overlapping of the class intervals is
avoided. Both the lower and upper limits are included in the class
interval. This type of classification may be used for a grouped
frequency distribution for discrete variable like members in a
family, number of workers in a factory etc., where the variable may
take only integral values. It cannot be used with fractional values
like age, height, weight etc.
This method may be illustrated as follows:
Class interval
Frequency
5 9
7
1014
12
1519
15
2029
21
3034
10
3539
5
Total
70
Thus to decide whether to use the inclusive method or the
exclusive method, it is important to determine whether the variable
55 under observation in a continuous or discrete one. In case of
continuous variables, the exclusive method must be used. The
inclusive method should be used in case of discrete variable.
c) Open end classes:
A class limit is missing either at the lower end of the first
class interval or at the upper end of the last class interval or both
are not specified. The necessity of open end classes arises in a
number of practical situations, particularly relating to economic and
medical data when there are few very high values or few very low
values which are far apart from the majority of observations.
The example for the openend classes as follows :
Salary Range
No of
workers
Below 2000
7
2000 – 4000
5
4000 – 6000
6
6000 – 8000
4
8000 and
3
above
4.5 Construction of frequency table:
Constructing a frequency distribution depends on the nature
of the given data. Hence, the following general consideration may
be borne in mind for ensuring meaningful classification of data.
1. The number of classes should preferably be between 5 and
20. However there is no rigidity about it.
2. As far as possible one should avoid values of class intervals
as 3,7,11,26…
.etc.
preferably one should have classintervals of either five or multiples of 5 like 10,20,25,100
e...
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 Winter '08
 Moshiri
 Business, Statistics

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