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Unequal sample sizes

When Unequal Sample Sizes Are and Are NOT a Problem in ANOVA

by Karen Grace-Martin 219 Comments

Updated Dec 18, 2020 to add more detail

In your statistics class, your professor made a big deal about unequal sample sizes in one-way Analysis of Variance (ANOVA) for two reasons.

1. Because she was making you calculate everything by hand.  Sums of squares require a different formula* if sample sizes are unequal, but statistical software will automatically use the right formula. So we’re not too concerned. We’re definitely using software.

2. Nice properties in ANOVA such as the Grand Mean being the intercept in an effect-coded regression model don’t hold when data are unbalanced.  Instead of the grand mean, you need to use a weighted mean.  That’s not a big deal if you’re aware of it. [Read more…] about When Unequal Sample Sizes Are and Are NOT a Problem in ANOVA

Tagged With: analysis of variance, ANOVA, SPSS, Unequal sample sizes

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