Tuesday, 15 December 2009

Cochran Test

This homogeneity of variance test is computationally less complex than the Bartlett test but is also subject to problems in non-normal conditions (Phil, 1999). The test statistic for the Cochran test is:

clip_image002 (F 2.21)

In this equation (F 2.21), clip_image004 is defined as:


Such that under the null hypothesis (clip_image008), the COC test statistic has an asymptotic distribution with K-1 degrees of freedom and a clip_image010central variable (Hartung, 2001). It has been shown that the Cochran test is suitable for equally sized samples and has good power in selected cases (Gartside, 1972).

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