AP Statistics / Unit 3: Inference for Categorical Data: Proportions
3.14 Setting Up a Chi-Square Test for Homogeneity or Independence
Notes
- Homogeneity: compare a categorical variable's distribution across several groups (separate samples).
- Independence: check for association between two categorical variables (one sample).
- Expected count $\displaystyle =\frac{\text{row total}\times\text{column total}}{\text{grand total}}$; all should be at least 5.
Practice
One sample of 500 people classified by age group and music preference. Test:
One sample, two variables.
Row total 40, column total 50, grand total 200. Expected count:
$\displaystyle \frac{40\cdot50}{200}$.
Separate random samples of 3 schools, comparing lunch choices. Test:
Several groups, one variable.
Ready for more? Take the Unit 3 test.