OUTLIER CALCULATION USING INTERQUARTILE RANGE
Steps
1. Arrange data in order.
2. Calculate first quartile (Q1)
3. Calculate third quartile (Q3)
4. Calculate interquartile range (IQR)
5. Calculate lower bracket
6. Calculate upper bracket
7. Anything outside the lower and upper
bracket is an outlier.
Calculating first quartile (Q1)
Calculating third quartile (Q3)
How to do in Excel
sort in ascending order
=QUARTILE, Array (all your data values,
Quartile=1
=QUARTILE, Array (all your data values,
Quartile=3
Q3-Q1
=Q1-(1.5 * IQR)
=Q3+(1.5 * IQR)
Example
Data Set Outlier?
25.0 FALSE
Example
24.6
26.1
FALSE
32.9
8.3
12.15
45.35
32.0
27.7
11.6
28.5
FALSE
FALSE
TRUE
FALSE
24.6
33.2
41.2
36.1
18.9
19.5
48.0
24.6
FALSE
FALSE
FALSE
FALSE
FALSE
FALSE
TRUE
FALSE