Transcription of Tests for Homogeneity of Variance - Montana State University
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Tests for Homogeneity of Variance - Montana State University
For Homogeneity of Variance In an ANOVA, one assumption is thehomogeneity of Variance (HOV)assumption. That is, inan ANOVA we assume that treatment variances are equal:H0: 21= 22= = 2a. Moderate deviations from the assumption of equal variances do not seriously affect the results in theANOVA. Therefore, the ANOVA is robust to small deviations from the HOV assumption. We onlyneed to be concerned about largedeviations from the HOV assumption. Evidence of a large heterogeneity of Variance problem is easy to detect in residual plots. Residualplots also provide information about patterns among the Variance . Some researchers like to perform a hypothesis test to validate the HOV assumption. We will considerthree common HOV Tests : Bartlett s Test, Levene s Test, and the Brown-Forsythe Test. These Tests are not powerful for detecting small or moderate differences in variances. This is okaybecause we are only concerned about largedeviations from the HOV Bartlett s Test To perform Bartlett s Test:1.
SAS and Minitab will perform a WLS analysis. You just have to supply the weights. 60. 2.13.1 Weighted Least Squares (WLS) Example ... 3 16 3 9 3 18 3 16 3 7 3 14 3 13 Dose % 4 17 4 13 4 16 4 19 4 26 4 15 4 23 4 27 Dose % 5 22 5 30 5 27 5 32 5 32 5 43 5 29 5 26 The sample variances s2 i are s2 1 = s 2 2 = s 2 3 = s 2 4 = s 2 5 =
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