2. Experimental Research Tries
to Establish Cause and Effect
Selection of a good theoretical framework
Application of appropriate experimental
design
Use of correct statistical model and
analysis
Proper selection and control of
independent variables
Appropriate selection and measurement of
dependent variables
Correct interpretation of results
2
3. Three Criteria for Cause and
Effect
1. The cause must precede
the effect in time
2. The cause and effect must
be correlated with each
other
3. The correlation between
cause and effect cannot be
explained by another
variable
3
4. Reviewing Important Terms
Independent variable
Dependent variable
Categorical variable-(age, sex=not controlled)
Control variable-exclude
Extraneous variable
4
5. Types of Validity
Internal validity
External validity
Trade-off between internal and external validity
Series of experiments (studies)
5
8. Threats to External Validity
Reactive or interactive effects of testing
Interaction of selection biases and treatment
Reactive effects of experimental arrangements
Multiple-treatment interference
8
9. Controlling Threats to
Internal Validity
Randomization
– Real randomization
– Matched pairs (but not matched groups)
– Randomizing treatments or counterbalancing
Placebos
Blind setups
Double-blind setups
9
11. Controlling Threats to External
Validity
Selecting from larger population
– Participants
– Treatments
– Situations
Ecological validity-emulates the real world?
11
12. Types of Designs:
Pre-experimental Designs (invalid)
One-shot studies
T
O
One-group pretest-posttest
O1 T
O2
Statistical analysis? Dt
Static group comparison (one shot w/2 groups)
T
O1
--------------Statistical analysis? It
O
12
13. Types of Designs:
True Experimental Designs
Randomized-groups design
R
T
O1
Statistical analysis? It
R
O2
Extending the levels—randomized-groups
design
R
T1 O 1
Statistical analysis? Ab
R
T2 O 2
R
O3
13
15. Types of Designs:
True Experimental Designs, cont’d
A factorial design with a categorical factor (B)
R
A1
O1
B1
R
A2
O2
R
A3
O3
Statistical analysis? M
---------------------------R
A1
O4
B2
R
A2
O5
R
A3
O6
15
16. Types of Designs:
True Experimental Designs
Pretest-posttest randomized-groups
R
O1
T
O2
R
O3
O4 Statistical analysis? MFA
Extending the design on the RM factor
R
O1
T
O2 T
O3 Statistical analysis? MFA-RM
R
O4
O5
O6
16
17. Types of Designs:
True Experimental Designs, cont’d
Extending the pretest-posttest randomized
groups design on both factors
R
O 1 T1 O 2 T1 O 3
R
O4
R
O7
T2
O5
O8
T2
O6
O9
Statistical analysis? AN (covariate)
17
18. Types of Designs:
True Experimental Designs, cont’d
Solomon four-group design—purpose=pretest effects
R
O1
T
O2
R
O3
O4
R
T
O5
R
O6
Statistical analysis (factorial ANOVA)
No treatment
Treatment
Pretested
O4
O2
Unpretested
O6
O5
18
21. Quasi-Experimental Designs:
Ex Post Facto (discriminate)
This is one of the pre-experimental designs,
but with the treatment not under the control
of the experimenter.
T
O1
------------------ Statistical analysis? A
O2
21
23. Quasi-Experimental Designs:
Single Participant
Identify participant and follow over time.
Does the treatment produce the same
effect each time?
Are treatment effects cumulative, or does
participant return to baseline?
Does participant’s response become less
variable over treatment times?
23
24. Quasi-Experimental Designs:
Single Participant, cont’d
Is participant’s magnitude of response
sensitive to multiple treatment
applications?
Do varying intensities, frequencies, and
lengths of treatment produce varying
responses?
24
25. Next Class
Chapter 15
Abstracts tonight
Research Q?
3 intro paragraphs
1.
2.
3.
Rationale
Lit summary
Empty space and purpose
25
