Title: Spurious Relationship
1Spurious Relationship
- A correlation between two variables that have no
causal relationship both variables are caused
by another variable
2Example Water causes drunkenness.
- Once a group of students decided to study
empirically the causes of drunkenness. - They drank vodka and water. Got drunk.
- They drank rum and water. Got drunk.
- They drank scotch and water. Got drunk.
- They drank bourbon and water. Got drunk.
- They drank gin and water. Got drunk.
- Conclusion Water causes drunkenness
3Examples of spurious relationships
- Amount of ice cream sold and death by drowning
(units are months) - Number of doctors and number of people dying of
disease (by city) - Number of churches and number of homicides (by
city) - Number of libraries and number of people on drugs
(over time)
4What causes the price of rum?
- There is a positive relationship between the
salaries of Presbyterian ministers in
Massachusetts and the price of rum in Havana. - What is the causal mechanism?
5Causal Mechanism?
International business conditions prices and
salaries increasing everywhere
Ministers salaries
Price of rum
6Popular Study Smoking causes bad grades
- True or spurious?
- What could be the variable (or variables) that
drive both?
7News reports
- Bottled water causes healthier babies
- Drinking tea makes you less likely to contract
lung cancer
8Research question Does education cause political
tolerance?
- Many scholars have found a positive relationship
between political tolerance (support for liberty
for political enemies) and education. - Causal mechanism?
- As people are educated, they are introduced to
different kinds of people and perceived danger of
political enemies decreases. - As people are educated, they are socialized to
the correctness of constitutional rights.
9Alternative Explanation
- Political tolerance is actually caused by
cognitive sophistication, as measured by IQ. - Causal mechanism?
- It is difficult to reconcile the emotional
reaction to named political enemies (i.e. Nazis)
with constitutional rights and it takes a high IQ
to understand that democracy benefits from giving
liberties to bad people.
10Relationship between Education and Political
Tolerance
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
11Probability
- The probability of an outcome
- is the frequency of that outcome
- if the process were repeated a large number of
times - under similar conditions
12Relationship between Education and Political
Tolerance
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
13What is the probability of
- High political tolerance, given low levels of
education? - Low political tolerance, given medium levels of
education? - High political tolerance, given high levels of
education? - Low political tolerance, given low levels of
education?
14Controlling for IQ
15Education and Political Tolerance
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
16Education and Political Tolerance - High IQ
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
17Education and Political Tolerance - High IQ
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
18Education and Political Tolerance - Low IQ
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
19Education and Political Tolerance - Low IQ
High
Political Tolerance
Medium
Low
Low
Medium
High
Education
20Conclusion?
- What was the hypothesis?
- What was the alternative explanation?
- What do we conclude about the likely cause of
political tolerance?