Comparing plots

 

Groups of population can be compared using box and whisker plots. Overall visible spread and difference between median is used to draw conclusion that there tends to be a difference between two groups or not.

Comparing plots

Case 2: Formula

P=DBMOVS×100P=DBMOVS×100

·         Where −

·         PP = percentage difference

·         DBMDBM = Difference Between Medians.

·         OVSOVS = Overall Visible Spread.

Rules

·         For a sample size of 30 if this percentage is greater than 33% there tends to be a difference between two groups.

·         For a sample size of 100 if this percentage is greater than 20% there tends to be a difference between two groups.

·         For a sample size of 1000 if this percentage is greater than 10% there tends to be a difference between two groups.

Example

Problem Statement:

Describe the difference between following sets of data.

Sr. No.

Name

Set A

Set B

1

Max

12

15

2

UQ

10

13

3

Median

7

10

4

LQ

6

9

5

Min

5

6

Solution:

Consider the following diagram:

Comparing plots

OVS=13−6 =7 DBM=10−3 =4OVS=13−6 =7 DBM=10−3 =4

Apply the formula

P=DBMOVS×100 =47×100 =57.14P=DBMOVS×100 =47×100 =57.14

As percentage is over 33% thus there is difference between Set A and Set B. It is likely that Set B is greater than Set A.