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Mean Differences Slide 1 The ‘differences between group means’ is a topic I’m certain was covered in your basic statistics classes. The goal of this PowerPoint presentation predominantly is to remind you about the formulae needed to calculate differences between group means and differences between group proportions. Slide 2 Before I leave you to your own devices for the remaining slides, it’s important to remind you that it’s impossible to compare means between groups unless you have interval or ratio scaled data. When groups are small and the population standard deviation is unknown, you use a t test to compare group means. When groups are large, you use a Z test. Slide 3 (No Audio) Slide 4 One last point before I leave you to formulae notation and numerical examples: the null hypothesis. The null hypothesis always assumes that the means between the groups are identical. In other words, if you took the mean for one group and subtracted it from the mean of the other group, then the result would be 0 if the null hypothesis is not rejected (i.e., there’s no difference between group means). Slide 5 to Slide 25 (No Audio) Page | 1