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

Give it a try

On the form below, you can put this all together. As you fill out each column, click on the button below it to check your numbers. BTW, this is where having a calculator will come in handy. As long as you use 2 significant digits in your calculations, the program will fill in additional digits for you.

Once again, recall that there were 42 mon/fri sickdays out of 100.

	observed ("o")	expected ("e")	(o-e)	(o-e)2	(o-e)2/e
Monday/ Friday
Midweek
Total	100	100
Check

 

So now you have a number which the chi-square statistic for this test, also called the " chi-square-calc". It's the one that's obnoxiously flashing at you. But what do you DO with it? You know that a big number is bad (because it means that the data deviate alot from the model) and a small number is good (because it means the data doesn't deviate). But how big is big, or how small is small?

Before we answer that question, we need to take a brief detour to discuss degrees of freedom. After that, we can finally answer the question, are Dilbert's colleagues really out fishing on their long weekends?