1. Section 6.2 Establishing Causation

2. Explaining Association: Causation
a.) Causation –
a direct cause-and-effect relationship between two variables
Ex: Mother’s body mass index and daughter’s body mass index
b.) Even when direct causation is present, it is rarely a complete explanation of an association between two variables.

3. c.) Even well established casual relations may not generalize to other settings.
d.) ASSOCIATION DOES NOT MEAN CAUSATION!!

4. II. Explaining Association: Common Response
Lurking Variable –
a variable that is not among the explanatory or response variables (not measured in the study) and yet may influence the interpretation of relationships among those variables.
Common Response –
when a lurking variable affects (changes) both the explanatory (x) and response (y) variables.
Ex. GPA and ACT score.

5. III. Explaining Association: Confounding
Confounding Variable –
one whose effects on the response variable cannot be separated from another possible explanatory variable.
Ex. Attending religious services and living longer.
Confounding variables can be either explanatory variables or lurking variables.
Ex. Years of education and worker’s income.

6. IV. Establishing Causation
a.) Experiments (with randomization) are the best way to establish cause-and-effect relationships
b.) Sometimes you cannot use experiments to establish cause-and-effect relationships.
Ex. Does praying make you live longer?
Does smoking cause lung cancer?

7. Criteria for establishing Causation (without experiments)
c.) Just because there is a lack of evidence does not necessarily mean there is no cause-and-effect relationship.
Criteria for establishing Causation (without experiments)
The association is strong
The association is consistent
Larger values of the response variable are associated with stronger responses.
The alleged cause precedes the effect in time.
The alleged cause is plausible.
Careful examination of lurking variables.

9. Causation: The amount of alcohol consumed and the blood alcohol level.
Examples:
Causation: The amount of alcohol consumed and the blood alcohol level.
2. Common Response: Student’s SAT score and college GPA are highly correlated. However, there is a lurking variable present that is affecting both the SAT and GPA. Students who are smart and who have learned a lot tend to have both high SAT scores and high college grades.

10. 3. Common Response: The number of ministers in Massachusetts and the price of rum in Havana are highly correlated. Lurking Variables: inflation, income increase, economy, etc. The lurking variable is affecting both the explanatory and response variables.
4. Confounding: Level of education and amount of income. It is likely that more education is a cause of higher income – many highly paid professions required advanced education. However, confounding is also present. People who have high ability and come from prosperous homes are more likely to get many years of education than people who are less able or poorer. Of course, people who start out able and rich are more likely to have high earnings even without much education. We can’t say how much of the higher income of well-educated people is actually caused by their education. You cannot separate (or take away) someone’s education

11. Activity
Exercises
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