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Q-test for Rejection of Outliers


Introduction

The Q-test is a simple statistical test to determine if a data point that is very different from the other data points in a set can be rejected. Only one data point may be discarded using the Q-test.

Q = |outlier - value closest to the outlier| / |highest value - lowest value|

Table of Q critical values (90% confidence)

N       QC
3      0.94
4      0.76
5      0.64
6      0.56
7      0.51
8      0.47
9      0.44
10     0.41

If Q is larger than QC the outlier can be discarded with 90% confidence.


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