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The "Good" Skittles Statistics Activity
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Lydia Ahlstrom (2025)
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I created this document for an activity in an introductory statistics class. Every student receives a ziplock bag of 30 Skittles (this is a random sample). I tell them the "good" Skittles are purple and red (noting that this may be biased). The manufacturer, Mars Inc., claims that each color is produced equally, so 40% of Skittles should be "good".

I ask them to perform a two-tailed z-test for the proportion of "good" Skittles using their sample data at the 0.05 significance level. I also ask them to construct a 95% confidence interval for the proportion of "good" Skittles.

Once they have counted their good Skittles, I ask them to report the count to me. I am able to enter each count in the first column, and a 95% confidence interval will automatically be constructed for each sample. We can then see how many of our ~20 intervals contain (what turns out to be) the true population proportion, 0.40.
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