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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 appears to be very different from the rest of the data points in a set may be discarded. Only one data point in a set may be rejected using the Q-test. The Q-test is:

q-test

The value of Q is compared to a critical value, Qc.

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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