1. -Correlation does not equal causation
-necessary but not sufficient
-Where there’s smoke there may be fire
Experimental approach attempts to create conditions where third variable effects and issues of directionality can be eliminated.

2. But what conditions would define a causal relationship?

3. Mills’ Canons of Causality conditions that must be met if a relationship is causal
Where “A” is presumed cause and “B” is presumed effect.
Method of agreement
Method of disagreement
Method of concomitant variation
Method of multiple causality

4. Method of Agreement
If “A” is present then so should be “B”

5. Method of Disagreement
If “A” is not present then neither should be “B.”

6. Method of concomitant Variation
If “A” is varied in intensity then “B” should show corresponding variation

7. How do we set up experimental conditions to test Mills assumptions

8. The Experimental approach
Systematic manipulation (variation) of the presumed causal variable
Systematic measurement of the presumed affected variable
Under controlled conditions

9. Terminology
The presumed causal variable = the independent variable (IV)
The manipulated variable
The administered variable
The presumed affected variable = the dependent variable (DV)
The measured variable

10. Identifying variables by “Titles.”
“The effects of Stress on attention.”
The Effects of Alcohol on social interaction.”
Marijuana increases attention to drug cues.”
Cognitive processing is diminished by nicotine.”
The relationship of reported drug use to political affiliation.”

11. Identifying Correlational studies vs Experimental studies
Identifying Correlational studies vs Experimental studies. There should be clear inference of cause or effect in Experimental studies
The effects of peanut butter on…
Peanut butter increases…
Brain size is increased…
Typing speed is related to….

12. Manipulation of IV to test Mills assumptions
Minimally, the IV must have two Levels or conditions
Present/absent or High vs low
IV may have more than two levels-
Concomitant variation

13. The Experimental and Control Conditions
The control condition is both a point of comparison and
Helps control for possible unwanted effects of extraneous (confounding) variables.

14. BASIC EXPERIMENTAL DESIGNS
Between group designs
Within group designs

15. Between vs Within Both use groups of subjects
Between groups test different groups at same time. Each group exposed to different level of IV
Within groups use same subjects tested repeatedly across different conditions of IV.

16. Design decision making
Fewer subjects
More time

17. The Experimental approach
Systematic manipulation (variation) of the presumed causal variable
Systematic measurement of the presumed affected variable
Under controlled conditions

18. Extraneous variables

19. Extraneous variables may become confounding variables

20. Confounding variables: An extraneous variable that varies with the IV.

21. Confounding variables
“ a variable that should be extraneous, but becomes systematically varied along with the IV.
Eg…”Effects of marijuana on memory.”
MJ accidentally administered only to experienced users but not to naïve users.

22. Experimental Control Procedures to minimize CVs
By elimination, constancy or specific testing of suspected confounds
The Control group or condition
= point of comparison and..
A fundamental control procedure