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Hartley's and Cochran's tests
for homogeneity of varianceOn this page: Hartley's Fmax test Cochran's test
Hartley's Fmax test
Hartley's Fmax test is probably the simplest test of homogeneity of variances. It is not very sensitive to departures from homogeneity, but some statisticians (for example Winer
The statistic Fmax is calculated as the ratio of the largest and smallest variances of the (k) groups each containing (n) observations:
Most tables are only for equal numbers of replicates, but Gill
Hartley's Fmax test assumes that the data for each group are normally distributed. It is apparently quite sensitive to violations of this assumption, so it should not be used on heavily skewed data.
Cochran's test is another relatively simple homogeneity of variance test. It uses the ratio of the largest variance to the sum of the variances as the test statistic. Since it uses more information it is, not surprisingly, more powerful than Hartley's Fmax test - at least for small equal sample sizes.
A table of critical values of C (with k and n-1 degrees of freedom) is provided in Winer