Experiments and Quasi Experiments Psychology

1. Experiments and Quasi
Experiments
Profesor Alexander Settles

2. Types of Experiments
There are four kinds of experiments:
–True experiments
–Quasi-experiments
–Natural experiments
–Naturalistic experiments

3. True Experiments
• Some true experiments are done
in the lab, others are done in the
field.
• There are five steps to follow in
conducting true experiments:

4. True Experiments
1. Need at least two groups: an experimental
group and a control group. One groups
gets the intervention, the other group does
not.
2. Random assignment of individuals to the
groups. (The degree to which random
assignment ensures equivalence of the
groups is dependant upon the size of the
groups.)

5. True Experiments
3. The groups are measured on one or more
dependent variables. This is called the
pretest.
4. The intervention (independent variable) is
introduced.
5. The dependent variables are measured
again. This is the post test.

6. Quasi-Experiments
• Are experiments where the ability to
randomly assign individuals to the
experimental and control groups is limited
or nonexistent.
• Quasi-experiments are more commonly
used in evaluating management policy

7. Quasi-Experiments
Example
In a study of the effectiveness of a new
management technique one branch office
is given a new TQM method to
implement another branch office retains
the traditional management policy

8. Quasi-Experiments
Example (cont.)
At the end of the a year the branch with
TQM has higher quality of production
than the one that retained the traditional
management technique.
Is this a “quasi-experiment”? Why?

9. Quasi-Experiments
Example (cont.)
Answer: Most likely -- YES
Random assignment to the two classes
was probably not made, hence, groups
may not be equivalent. Possibility of
results being confounded other factors
remains.

10. Natural Experiments
Natural experiments are happening
around us all the time. They are not
conducted by researchers, but simply
evaluated by researchers. In other words,
the researcher does not have control over
the application of the treatment. This also
means that there is no control over what
groups receive the treatment and the
composition of those groups.

11. Naturalistic Experiments
In naturalistic experiments, one
contrives to collect experimental
data under natural conditions. You
make the data happen out in the
natural world (not in the lab), and
you evaluate the results.

12. Naturalistic Experiments
The difference between a natural
experiment and a naturalistic
experiment is that the first just
happens, the second must be
contrived to happen.

13. Naturalistic Experiments
Naturalistic experiments deviate
from true experiments because
group membership is not randomly
assigned, and exogenous factors
(confounding variables) are not
controlled.

14. Naturalistic Experiments
Examples:
• Patience of drivers behind a car that did not move
soon after a red light turned green (independent
variables: newness of car and dress of driver)
• Matched pair testing to uncover discrimination in
hiring practices
• Determining a manager’s fulfillment of new learning
organization policy by placing an employee in the
team with training and monitoring responsibility