Section1:
2
x 2 Tables
Chi-Square
Degrees of Freedom
p-Value
Flip Coin 100 times
Breast Cancer Example
Comparison in Simple 2 x 2 Tables
So-called 2 x 2 tables arise frequently in empirical work, both inside and outside of law.
We start with some non-law-related examples, and then apply what you have learned to a legal setting.
Coin Example
Consider two coins, A and B.
Each are flipped 10 times, with the following results:
|
|
 Number of Heads |
 Number of Tails |
|
|
Coin A |
5 |
5 |
10 |
|
Coin B |
7 |
3 |
10 |
|
Totals |
12 |
8 |
20 |
Suppose we think that the coins have the same probability of heads and tails.
Question
Can we reject the hypothesis that the variation we observe, 50 percent heads for one coin versus 70 percent heads for the other coin, occurs by chance? That is, what does your intuition tell you?
