Table of Contents

• Prequiz...
• 1: Do those shoes fit?
• 2: Dilbert's 3 day work week
• 3: The day is saved . or not
• 4: The Brute Force method
• 5: Computer = brute force
• 6: What's your threshold for pain?
• 7: Sick-day sistribution
• 8: A brief recap of the Brute Force Method
• 9: The Brute Force method again
• 10: Using arithmetic instead of Brute Force
• 11: One small correction
• 12: How big is big?
• 13: Degrees of Freedom
• 14: The magic lookup table
• 15: The answer, finally
• 16: Summary of chi-square
• 17: Another example for chi-square
• 18: So, which method do you like better?
• 19: Applications
• 20: Example 1: Testing for a dihybrid ratio
• 21: Example 2: Habitat selection (ecology)
• 22: Review and Words of Wisdom

The day is saved … or not

Apparently we have saved the day. 40% of sickdays SHOULD fall on Monday or Friday, which means that employees are not abusing the system.

But wait. What if next year, Evil Pointy-Haired Boss (EPHB) finds that 42% sickdays fell on Monday or Friday??? Proof positive, in his view, that employees are out to get him.

Let's be Dilbert for a minute. How could we confirm or disprove Evil Pointy-Haired Boss (EPHB's) claim? Clearly 42% is more than 40% -- but how much is too much? Do the extra 2% just represent the natural "slop" around 40%?

In fact there are (at least) two ways to do this:

1. The Brute Force method: make up ("simulate") lots of data. This is conceptually not too hard, but it requires a lot of computation.

2. The Statistical method: chi-square test. This is conceptually harder, but requires only basic arithmetic, a calculator, and a lookup table to implement.

We'll try them both, and you can see which one you like better.