1. Chapter 8 Control

2. Supplemental Information (Not in Textbook)
Control in experiments maximizes internal validity
High internal validity of research = ability to infer CAUSAL associations
Most correlations do not describe a causal relationship
Examples………..

3. Control by selection
“Attending a private schools correlates with better performance on standardized tests (versus attending public schools). “
As a result of this observation, many people believe that sending children to private schools will help increase test scores.

4. Control by selection
One of the problems with this inference is that there are other variables that could influence both the kind of school a kid attends and his or her test scores.
For example, the financial status of the family is a possible confound.
“quality” of school
test scores + +
financial status

5. Correlation and Causation
Amount of ice cream sold on the beach correlates with the number of drownings
What are some explanations?
Group discussions

6. Correlation and Causation
Amount of ice cream sold on the beach correlates with the number of drownings
What are some explanations?
Eating ice cream causes drownings (?)
People console themselves with ice cream when people drown (?)\
Third factor----increasing summer temperatue increases beach populations and hence, food sales (ice cream) and drownings

7. Correlation and Causation
Increases in number of people living in Louisiana correlates with increasing loss of land mass due to sinking
More people causes more weight atop the land and hence, more sinking of land in LA (?)

8. Correlation and Causation
Increases in number of people living in Louisiana correlates with increasing loss of land mass due to sinking
Coincidental association; geological forces cause sinking, with/without people atop the land.

9. Correlation and Causation
In 1974, a decrease in national speed limit to 55 is correlated with decreases in highway death rates the following year
A causal relationship here?

10. Correlation and Causation
In 1974, a decrease in national speed limit to 55 is correlated with decreases in highway death rates the following year
A causal relationship here?
No, middle eastern countries limited sales of oil to the US (an oil embargo). Price of gas increased, people drove less. Gas became less available (spot shortages) and people drove less. Fewer total drivers on the road per mile probably caused the decrease in highway deaths in 1975

11. What is Simpson’s Paradox?
This will be a question reflected in Exam 2

12. Supplement to Textbook
Social policy-makers, political leaders, science groups declare “causal associations” based on preponderance of evidence from a large body of less-than-optimal science and indirect evidence
Notion of Evaluating “Converging Evidence” to decide Causality

13. Example: Does Smoking Cause Lung Cancer?
Examples:
Lung Cancer and Smoking
Global Warming

14. Example: Does Smoking Cause Lung Cancer?
Examples:
Lung Cancer and Smoking
Optimal experimental design regarding smoking and lung cancer cannot be conducted for practical and ethical reasons
What would such a study look like?
Discuss, explain

15. Example: Does Smoking Cause Lung Cancer?
Criteria used by Surgeon General’s commission on smoking in 1964
Strength of the association
Example Consistently, we find that smokers are many times more likely to develop lung cancer than nonsmokers
Consistency of the association
Example: diverse correlational studies show the same association

16. Example: Does Smoking Cause Lung Cancer?
Criteria used by Surgeon General’s commission on smoking in 1964
Specificity of the association
Example: speculations about other possible causal factors prove to be in error when any of these other causal factors are studied and controlled for e.g., living in urban area with polluted air
Example: lung cancer rates can be predicted from smoking data and smoking is found to predict lung cancer

17. Example: Does Smoking Cause Lung Cancer?
Criteria used by Surgeon General’s commission on smoking in 1964
Temporal relationship of the association
Cancer always follows smoking behavior, not vice versa
Once people in a population stop smoking, rates of lung cancer subsequently decrease over time

18. Example: Does Smoking Cause Lung Cancer?
Criteria used by Surgeon General’s commission on smoking in 1964
Coherence of the association
Example: all available animal and human studies suggest the association exists between smoking and cancer in animals and humans; scientific findings about the nature of carcinogens and causes of cancer support the association

19. Interpreting Correlations (Supplement to Textbook)
Correlation between teachers’ salaries and the amount of liquor sold
Increased drinking caused by increasing salaries among teachers?

20. Control Ways to rule out threats to validity Two basic meanings:
Standard for comparison
Minimizing variability

21. How to Increase Experimental Control
Use a lab, if possible
Consider the experimental setting
Instrumentation for measuring responses
Make nuisance variables into IVs
Statistical control
Replicate your findings

22. Basically 2 Types of Experiments
Within-Subjects Experiment
Each subject experiences ALL experimental conditions.
Between-Subjects Experiment
Each subject experiences only ONE experimental condition

23. Control in a Within-Subjects Design
Each subject is used as their OWN control.
Control Condition
Occasion when the subject DOESN’T get the IV.
Experimental Condition
The subject gets the IV.
The participant’s scores (DV) on the control condition are compared to those from the experimental condition.

25. Control in a Between-Subjects Design
Experimental Group
Subjects who get the IV
Control Group
Subjects who DON’T get the IV
Random Assignment
Every subject has an equal and independent chance to be in a group.
Matching
Making sure that the experimental and control groups are equal on one or more variables BEFORE the experiment starts.