Contents
- 1 Is the homogeneity of variance assumption violated?
- 2 What does it mean when the assumption of homogeneity of variance is violated and what can be done when it is a big problem and when is it a small problem?
- 3 Can a one way ANOVA tolerate a violation?
- 4 What to do when data fail tests for homogeneity of variance?
Is the homogeneity of variance assumption violated?
If sample sizes are equal, the pooling of variances will yield the same result. However, when sample sizes are unequal, the pooling of variances can cause quite different results. When this null hypothesis is not rejected, then homogeneity of variance is confirmed, and the assumption is not violated.
What does it mean when the assumption of homogeneity of variance is violated and what can be done when it is a big problem and when is it a small problem?
If group sizes are vastly unequal and homogeneity of variance is violated, then the F statistic will be biased when large sample variances are associated with small group sizes. When this occurs, the significance level will be underestimated, which can cause the null hypothesis to be falsely rejected.
What are the assumptions of a two way ANOVA?
To use a two-way ANOVA your data should meet certain assumptions.Two-way ANOVA makes all of the normal assumptions of a parametric test of difference: The variation around the mean for each group being compared should be similar among all groups.
When to use homogeneity test in ANOVA?
Homogeneity tests for equality of variances. If p > 0.05, equal variances can be assumed If p < 0.05, the results of the ANOVA are less reliable. There is no equivalent test but comparing the p-values from the ANOVA with 0.01 instead of 0.05 is acceptable.
Can a one way ANOVA tolerate a violation?
This means that it tolerates violations to its normality assumption rather well. As regards the normality of group data, the one-way ANOVA can tolerate data that is non-normal (skewed or kurtotic distributions) with only a small effect on the Type I error rate.
What to do when data fail tests for homogeneity of variance?
What to do when data fail tests for homogeneity of variance (part of one-way ANOVA)? One-way ANOVA assumes that the data come from populations that are Gaussian and have equal variances. GraphPad Prism tests this assumption with Bartlett’s test.