1. Warm Up
Check your understanding on p. 711 – Just do #2

2. Using the calculator to do a chi-square test of homogeneity…
Enter the observed and expected data into two separate matrices
Remember: The calc will do this for you when you select the test. 

3. Example:
A recent study tracked the television viewing habits of 100 randomly selected first-grade boys and 200 randomly selected first-grade girls. Each child was asked to identify their favorite TV show. The following table summarizes the results:
Expected values in red
Do these data provide convincing evidence that television preferences differ significantly for boys and girls?
Plugging into the calculator yields the following results:
Zooboomafoo
iCarly
Phineas & Ferb
Boys 20 30 50
Girls 70 80 30 36
33.3 60
73.3
66.6

4. Follow-Up Analysis – Does music influence what customers buy?
The chi-square test for homogeneity allows us to compare the distribution of a categorical variable for any number of populations or treatments. If the test allows us to reject the null hypothesis of no difference, we then want to do a follow-up analysis that examines the differences in detail. Start by examining which cells in the two-way table show large deviations between the observed and expected counts. Then look at the individual components to see which terms contribute most to the chi-square statistic.
Looking at the output, we see that just two of the nine components that make up the chi-square statistic contribute about 14 (almost 77%) of the total χ2 =
We are led to a specific conclusion: orders of Italian entrees are strongly affected by Italian and French music.

5. Follow Up Analysis for TV Show Problem
Conduct a follow-up analysis of the TV show problem.
A follow up analysis suggests the biggest difference occurs in the preferences occurs in the preferences for Phineas and Ferb, with more boys and fewer girls preferring the how than expected.