1. Categorical Variables
Section 2.1
Categorical Variables

2. Review
Suppose we were to find some interesting relationships in data collected in a survey given to all of you. Could we make any conclusions about causality? (a) Yes (b) No (c) It depends on the data
Survey data are observational – cannot make conclusions about causality.
Make this explicitly about their class survey data if you collected data from them.

3. Review
Suppose we were to find some interesting relationships in data collected in a survey given to all of you. Can we generalize the results of this sample to all students at this school? (a) Yes (b) No (c) It depends on the data
The sample is not random, and not representative of the population.
Replace “this school” with your school

4. Two-Way Table
Female
Male
Total
In a Relationship 32 10 42
It’s Complicated 12 7 19
Single 63 45
108
107 62
169
42/169  25%
32/107  30%
10/62  16%
32/42  76%
What proportion of students in this sample are in a relationship?

5. Two-Way Table
Female
Male
Total
In a Relationship 32 10 42
It’s Complicated 12 7 19
Single 63 45
108
107 62
169
42/169  25%
32/107  30%
10/62  16%
32/42  76%
What proportion of females in this sample are in a relationship?

6. Two-Way Table
Female
Male
Total
In a Relationship 32 10 42
It’s Complicated 12 7 19
Single 63 45
108
107 62
169
42/169  25%
32/107  30%
10/62  16%
32/42  76%
What proportion of people in a relationship in this sample are female?

7. Two-Way Table
Female
Male
Total
In a Relationship 32 10 42
It’s Complicated 12 7 19
Single 63 45
108
107 62
169
42/169  25%
32/107  30%
10/62  16%
32/42  76%
What proportion of males in this sample are in a relationship?

8. What percent of participants had neither? 10% 20% 30% 50% 70%
Aspirin
Placebo
Total
Heart Attack 10 40 50
Stroke 20 30
Neither 70
100
200
What percent of participants had neither?
10%
20%
30%
50%
70%

9. What percent of heart attack victims took aspirin? 10% 20% 30% 50% 70%
Placebo
Total
Heart Attack 10 40 50
Stroke 20 30
Neither 70
100
200
What percent of heart attack victims took aspirin?
10%
20%
30%
50%
70%

10. What percent of aspirin takers had a heart attack? 10% 20% 30% 50% 70%
Placebo
Total
Heart Attack 10 40 50
Stroke 20 30
Neither 70
100
200
What percent of aspirin takers had a heart attack?
10%
20%
30%
50%
70%

11. What percent were taking a placebo, of those that had a stroke? 10%
Aspirin
Placebo
Total
Heart Attack 10 40 50
Stroke 20 30
Neither 70
100
200
What percent were taking a placebo, of those that had a stroke?
10%
20%
30%
50%
60%