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ANOVA

I have 4 groups of data that i need to compare. The data is reasonably normally distributed but the variance of each group is not equal, does this mean i cannot preform an ANOVA test? Any one shed any light?!
Reply 1
Avatar for titanlux
titanlux
6
That¡s what ANOVA is for... to check whether the variances differ significantly
Reply 2
Avatar for gemmared
gemmared
OP
this is what i thought, however .. 'Equality (or "homogeneity") of variances, called homoscedasticity — the variance of data in groups should be the same. Model-based approaches usually assume that the variance is constant. The constant-variance property also appears in the randomization (design-based) analysis of randomized experiments, where it is a necessary consequence of the randomized design and the assumption of unit treatment additivity (Hinkelmann and Kempthorne 2008): If the responses of a randomized balanced experiment fail to have constant variance, then the assumption of unit treatment additivity is necessarily violated.'
Reply 3
Avatar for titanlux
titanlux
6
In essence your null hypothesis is that the variance is statistically similar. The ANOVA is used to either disprove this or suggest further evidence is necessary
Reply 4
Avatar for Rosie18
Rosie18
9
If your data does not have homoscedasity (e.g. the variance within the groups is not the same.. As shown by something like the Levenes test) then a fundamental assumption of ANOVA is broken. Subsequently, your risk of type I error is elevated (based on a number of things including the relative sample sizes).

Your choices basically include performing some transformations or using a non-parametric alternative such as the kruskal wallis (depending on what design you're using).

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