# Method of forming Class Interval || Describing Data: Graphs and Tables || Bcis Notes

## Methods of forming Class Interval

There are two methods of forming class intervals like exclusive method and inclusive method.

#### 1. Exclusive Method

The formation of the class interval by this method is that if the upper limit of one class is the lower limit of the next class so as to continue without any gap.

Examples:

• 10-20
• 20-30
• 30-40
• 40-50

#### 2. Inclusive Method

The formation of the class interval by this method is that if both lower limits and upper limits are included in a particular way.

Examples:

• 10-19
• 20-29
• 30-39
• 40-49

To convert the class of inclusive type into that of exclusive type.

The correction factor denoted by cf and is given by:

Real Upper Limit = Upper limit + cf

Real Lower Limit = Lower limit – cf

#### Open-ended Classes

In case of continuous frequency distribution if the lower limit of the first-class or upper limit of the last class isn’t specified or missing those classes are called open-ended classes.

For Example:

Wage                                       No. of Workers

Less than 10                                   5

10 – 20                                            10

20 – 30                                           15

30 – 40                                           20

40 – 50                                            8

50 – 60                                            5

#### Cumulative frequency distribution

There are two types of cumulative frequency, they are:

1. Less than cumulative frequency distribution
2. More than cumulative frequency distribution

#### 1. Less than Cumulative Frequency Distribution

Construct the less than the cumulative frequency of the following data:

Wage                                          No. of workers

Less than 10                                         5

Less than 20                                         15

Less than 30                                         30

Less than 40                                         50

Less than 50                                          58

Less than 60                                          63

#### 2. More than Cumulative Frequency Distribution

Q. Construct the more than the cumulative frequency of the following data:

Wage                                          No. of Workers

More than 0                                           63

More than 10                                         58

More than 20                                         48

More than 30                                          33

More than 40                                          13

More than 50                                          5

This is the concepts of Method of forming Class Interval

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