Levene's test

The assumptions of ANOVA are relatively simple. Similar to an independent t-test, we have a continuous dependent variable, which we assume to be normally distributed. Furthermore, we assume homogeneity of variance, which can be tested with Levene's test.

It's good practice to check both assumptions before you do ANOVA, but here we'll focus on the latter. If the assumptions don't hold, then the ANOVA results won't be valid.

Perform Levene's test for the working memory data wm. Use leveneTest from the car package with the dependent and independent variables as first and second arguments, respectively.
If you don't specify additional arguments, the deviation scores are calculated by comparing each score to its group median. This is the default behavior, even though they are typically calculated by comparing each score to its group mean. If you want to use means and not medians, add an argument center = mean. Do this now and compare the results to the first test.

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Exercise

Levene's test

Instructions