1. CHAPTER 8
EXPERIMENTS

2. EXPERIMENTS INVOLVE 1. Taking Action
2. Observing the Consequences of that Action.
Especially relevant for hypothesis testing
Effective way to determine causation.
Studying small group interaction
Can be done in a natural setup- experiments that occur in the regular course of social events are “natural experiments.”

3. Three components of the experiment
1. Independent and dependent variables
2. Pretest and Posttest
3. Experimental and Control Groups

4. 1. Independent and Dependent Variables:
Independent variable- the experiment stimulus which is either present or absent
The dependent variable is the one that is affected by the stimulus.
Both independent and dependent variables must be operationally defined, i.e. how they are going to be observed in an objective (i.e. standardized/reliable) manner.
E.g. showing a group of subjects a movie about black history and measuring its effect on prejudice

5. 2. Pre-testing and Post-testing:
Pretesting involves measuring the subjects in terms of the dependent variable before application of the stimulus (independent variable)
Posttesting involves measuring the same subjects in terms of the same dependent variable after the application of the stimulus (independent variable)
Note: the Hawthorne effect: the very act of studying something might change it.

6. 3. Experimental and Control Groups
For an experiment to have scientific validity it must be double blind i.e have an experimental and control group where neither the subjects nor the researcher knows which one is the control and which one is the experimental group.
Having a control group means that the researcher can assess after the experiment any effects that were a result of the experimental process itself.

7. Basic Experiment Design Same Different
Experimental Group
Control Group
Stimulus
Remeasure Dependent
Remeasure Dependent

8. Control groups can guard against the effects of events outside the laboratory
In order for the control group to be an effective guard against bias, both the experimental and control groups must be as similar as possible, at the very least on those variables thought to be related to the dependent variable.
Generalizability is always a problem in experiments given a small sample size.

9. Experimental Design Variation:
1.Preexperimental Research Design
One shot case study: Administer the stimulus and measure the dependent variable. A crude form of “experiment”
One-group pretest-posttest design: measure the dependent variable before and after the administration of the stimulus but there is no control group, which does not let us guard for experiment effects.
Static group comparison: no pretest, stimulus to experimental group and both exp group and control group measured after stimulus.

10. Internal Invalidity in Experiments:
The experiment results might not accurately reflect what has gone on in the experiment.
1. History: an event that confounds the experiment result
2. Maturation: growing and changing- results.
3. Testing: retesting influences people’s behavior to confound the experiment’s results.

11. 4. Instrumentation: the measures of the pretest and posttest instrument are altered.
5. Statistical Regression: Start out with extreme scores and regress to the mean.
6. Selection biases of control and experimental groups
7. Experimental mortality: people dropping out of the experiment during its course. 8. Causal time order: did the dependent variable cause changes in the stimulus or did the stimulus cause changes in the dependent variable.

12. 9. Diffusion of treatment: communication between control and experimental group 10. Compenstaion: not receiving the treatment might result in some form of compensation for the control group producing unintended effect. 11. Compensatory rivalry between control and experimental groups 12. Demoralization of the control group more so than the experimental group.

13. II. Sources of External Invalidity
Refers to the generalizability of experimental findings to the “real” world.
Interaction between testing and stimulus- will the experimental results be valid in a “natural setting.”
Solomon Four Group Design (to guard against interact)on between testing and stimulus.

14. Sources of External Invalidity
This refers to the generalizability of experiment findings to the ‘real’ world.
Interaction between the testing situation and the experimental stimulus.
To control for this we have a special experiment design called the “Solomon four group design.”

15. The Solomon Four Group Design
Four groups of subjects assigned randomly from a pool of subjects.
Groups 1 and 2 are the classical experiment design based control and experimental groups with pretests and posttests.
Group 3 gets the experimental stimulus without a pretest
Group 4 is only posttested without a pretest and stimulus.

16. The results should reveal
Group 1 has posttest scores that reveal effect of stimulus by being different to group 2
Group 3 without a pretest should also have different scores on the posttest compared to group 2
Group 4 should have the highest or lowest scores on the posttest since it has no pretest or stimulus and precludes any experimental interaction (posttest only design).

17. Natural Experiments
Experiment that occurs in the course of ‘normal’ social events
E.g. studying people’s attitudes before and after a disaster
Major weakness of experiments:
Artificial
Interaction between experimental stimulus and experiment design
Major Strength of experiments:
1. Offers control of the independent variable in order to establish causation

18. Ethical Considerations
Experiments almost always involve deception, the double blind design that is needed for validity means that the group which gets the treatment does not know it, neither does the group that gets the placebo or pseudo-treatment know it.
Intrusive- involve people going through unusual experiences that might harm them even if such harm is not anticipated.