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# lab7 - Analysis of Variance Allows us to test the...

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1 Analysis of Variance Allows us to test the difference in means for more than two groups. – Tedious to do multiple t -tests – Increase your alpha error, even if you think you are keeping it at .05 (or whatever level you initially choose) Null and alternative hypotheses 0 1 3 2 1 0 : : H H H k not µ µ µ µ L = = = Use the F statistic to test for the difference in means Why use a ratio of variances to test for a difference in means ? Sources of variance Between Groups : If you have multiple groups, each will have its own mean, and there will be an overall (grand) mean as well. Each of the group means will differ from the grand mean, leading to a positive variance of group means from the grand mean Within Groups : Individual scores will vary from their particular group mean If the variance of the group means from the grand mean is much bigger than the individual variance, then you have evidence that there are differences in group means.

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