AP Statistics / Unit 2: Probability, Random Variables, and Probability Distributions
2.2 Summary Statistics for Two Categorical Variables
Notes
- Joint relative frequency: cell ÷ grand total.
- Marginal relative frequency: row or column total ÷ grand total.
- Conditional relative frequency: cell ÷ its row or column total.
- If conditional distributions differ, the variables are associated.
Practice
30 of 50 seniors drive; 10 of 50 juniors drive. Proportion of seniors who drive:
$\displaystyle \frac{30}{50}$.
Using those numbers, is driving associated with grade?
Different conditional distributions suggest association.
A joint relative frequency divides a cell count by:
Joint means out of everyone.
Ready for more? Take the Unit 2 test.