Contingency tables
Hair color
black
brown
blonde
marginal sums
Eye color
blue
12
45
14
71
brown
51
256
84
391
marginal sums
63
301
98
grand total: 462

2 x 2 Tables

Var2

level 1
level 2
 Sums
Var 1
level 1
f11
f12
R1
level 2
f21
f22
R2

 Sums
C1
C2
n
.

Odds and Odds-ratios
•Allow a detailed analysis of contingency tables beyond the rejection of independence of the two
variables
•Useful for n x 2 tables
•Based on a subdivision of the table into several 2 x 2 tables
•Odds = probability of one outcome of a variable within one category of the other variable
•Odds ratio = ratio of two odds
•Can be tested for significance
•
•
•
Hair color
black
brown
blonde
marginal sums
Eye color
blue
12
45
14
71
brown
51
256
84
391
marginal sums
63
301
98
grand total: 462
Odds blue eyes in black-haired people = 12/63 = 0.19
Odds blue eyes in brown-haired people = 45/301 = 0.15
Odds ratio (blue-eyed in black vs. brown-haired people)= 0.19/0.15 = 1.27