Table of Contents

• 1: Do those shoes fit?
• 2: Dilbert's 3 day work week
• 3: The day is saved ... or not
• 4: What you observe vs expect
• 5: The Chi-squared Equation
• 6: Give it a try
• Detour
• 7: What's a p-value?
• 8: What's a Lookup Table?
• 9: What's a "df"?
• Completing the Chi-squared Test
• 10: Interpreting a chi-squared
• 11: The answer, finally
• 12: Summary
• 13: What about 90% M/F sick days?
• 14: What about 50% M/F sick days?
• Chi-squared in Biology
• 15: Testing for a dihybrid ratio
• 16: 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. By the way, this is where having a calculator will come in handy. As long as you use two significant digits in your calculations, the program will fill in additional digits for you.

Once again, recall that there were 42 Monday and Friday sick days 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 calculated a number which is the chi-squared statistic for this test; it is 0.167. But what do you DO with it? You know that a big chi-squared statistic is bad (because it means that the data deviate a lot from the model) and a small chi-squared statistic 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?