1. Ch. 7: Randomized Experiments and Causal Inference

2. Randomized Experiments
Experiments where participants are randomly assigned to the experimental groups or conditions.
Often referred to as “true experiments.”

3. Reasons for Using Random Assignment
Provides a safeguard against biased assignment of sampling units to the different treatment groups.
Distributes the characteristics of the sampling units over the different conditions to prevent biased outcomes.
Permits the use of statistical analyses that require certain data characteristics.

4. Ways of Achieving Random Assignment
Presorting booklets or questionnaires
Blindly drawing names
Flipping a coin
Consulting a table of random numbers

5. Between-Subjects Designs
Subjects are exposed to one condition each.
Also called nested designs.
Condition A
Condition B
Subject 1
Subject 2
Subject 3
Subject 4
Subject 5
Subject 6
Subject 7
Subject 8
Subject 9
Subject 10

6. Within-Subjects Design
Subjects are exposed to each condition.
Also called:
Repeated-measures design
Crossed design
Importance of counter-balancing
Condition A
Condition B
Subject 1
Subject 2
Subject 3
Subject 4
Subject 5
Subject 6
Subject 7
Subject 8
Subject 9
Subject 10

7. Order of administration
Latin Squares Design
Order of administration 1 2 3 4
Sequence 1 A B C D
Sequence 2
Sequence 3
Sequence 4

8. Factorial Designs
Design has more than one factor and two or more levels of each factor
Manipulated
conditions
Gender
Drug
Placebo
Women A B
Men C D

9. Aristotle’s Four Kinds of Causation
Material
Formal
Final
Efficient

10. Three Criteria of Efficient Causation
Covariation
Temporal precedence
Internal validity

11. Mill’s Methods Method of agreement Method of difference If X, then Y.
X is a sufficient condition of Y.
Method of difference
If not-X, then not-Y.
X is a necessary condition of Y.

12. Mill’s Methods and the Simple Randomized Design
Experimental Group
Control Group
If X, then Y.
(Method of Agreement)
If not-X, then not-Y
(Method of Difference)

13. Solomon Four-Group Design
Pretested?
Experimentally
treated?
Yes No
Group I
Group II
Group III
Group IV

14. Plausible Causal Events in the Solomon Design
Plausible effects
Causal events
Group I
Group II
Group III
Group IV
Pretest
Yes No
Treatment
Sensitization
Extraneous effects

15. Diagramming the Solomon Design
Group I R O X
Group II
Group III
Group IV
R = Randomization O = Observation X = Treatment exposure

16. Preexperimental Designs
One-shot case study:
Symbolized as X-O
where X = treatment exposure and O = observation
One-group pre-post design
Symbolized as O-X-O

17. Examples of Potential Threats to Internal Validity
History
Maturation
Instrumentation
Selection

18. The Social Psychology of the Experiment
Artifact: A finding resulting from conditions other than those intended by the experimenter.
Demand characteristics & the good subject
Use of quasi-control subjects
Experimenter Expectancy Effect
Use of blind experimenters and double-blind procedures

19. Basic Expectancy Control Design
Expectancy conditions
Treatment
conditions
Experimental treatment
Control treatment
Experimental
Group A
Group B
Control
Group C
Group D

20. Burnham’s (1966) Use of the Expectancy Control Design
Expectancy conditions
Treatment
conditions
Lesioning of brain
No lesioning of brain
Row means
46.5
49.0
47.75
No lesioning of
brain
48.2
58.3
53.25
Column means
47.35
53.65