Day 22: Statistics for Business Applications

Last Time: Testing the difference in two means
Collect problems 12.4
Questions about old stuff?
Today: More on the difference between two means (independent samples)
- Today, we'll consider also the case of unequal variances. But first, we wrap up our consideration of the equal variance case.
- Example handout (assuming equal variances)
- Heights of NKU students: males versus females.
  - To capture the "distance" (in minutes) for the one person who didn't give a time, I used linear regression on the data that four people provided.
  - Men's distribution
  - Women's distribution
  - Both distributions
  - T-test for difference in means of heights
  - T-test for difference in means of "distances"
- In the case where the standard deviations are unequal,
  - the change is slight to the standard error
  - the change is great to the degrees of freedom (we lose additional degrees of freedom)
  - At this point is hard to say when to say they're unequal (just eyeball it!)
- Examples:
  - handout problem
  - #13.52
Next time: Start section 13.4 - Paired samples and inference about the difference of two means

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