1. Physical Variables
Social Variables
Personality Variables
Context Variables

2. What are physical variables?
Physical variables are aspects of the testing situation that need to be controlled:
day of the week
experimental room
lighting
Physical Variables

3. Physical Variables Explain elimination.
Elimination completely removes extraneous physical variables from the experimental situation (e.g., soundproofing a room).
Removal of extraneous physical variables prevents them from operating differently across different treatment conditions.
Physical Variables

4. How does constancy of conditions work?
Constancy of conditions controls extraneous physical variables by keeping all aspects of the treatment conditions identical, except for the independent variable. For example, test all subjects in the same room
or at the same time of day.
Physical Variables

5. How does balancing work?
Balancing controls extraneous physical variables by equally distributing their effects across treatment conditions.
For example, running half of the subjects in each condition in the morning and half in the evening.
Physical Variables

6. In which order should you use these techniques?
1. Eliminate extraneous variables whenever possible.
2. Keep conditions constant where elimination is not possible.
3. Balance the effects of extraneous variables
when constancy of conditions is not possible.
Physical Variables

7. What are social variables?
Social variables are aspects of the relationships between subjects and experimenters that can influence experimental results.
These include demand characteristics and experimenter bias.
Social Variables

8. Explain demand characteristics.
Demand characteristics are cues within the experimental situation that demand or elicit specific participant responses.
Example: students cue professors to wrap up their lectures by packing their binders, books, and water bottles, and by looking at the door.
Social Variables

9. How can demand characteristics threaten internal validity?
Demand characteristics can confound an experiment if they vary across experimental conditions. Subjects may act to confirm what they think is the experimental hypothesis.
Social Variables

10. What is a single-blind experiment?
In a single-blind experiment, subjects are not told their treatment condition.
For example, in a single-blind drug study, the experimental and control groups might receive capsules that look and taste identical.
Social Variables

11. How do single-blind experiments control demand characteristics?
When subjects are not told their treatment condition, this eliminates cues that might alter their behavior.
Social Variables

12. What is the placebo effect?
The placebo effect is when a subject receives an inert treatment and improves because of positive expectancies.
Social Variables

13. How do cover stories control demand characteristics?
A cover story is a false plausible explanation of the experimental procedures to disguise the research hypothesis from the subjects.
They should be used sparingly, since they are a form of deception.
Social Variables

14. What is experimenter bias?
Experimenter bias is any behavior by the experimenter that can confound the experiment.
For example, an experimenter might provide more attention to subjects in one condition than another.
Social Variables

15. What is the Rosenthal effect?
The Rosenthal effect is the phenomenon in which experimenters treat subjects differently based on their expectations and their resulting actions influence subject performance.
This is also called the Pygmalion effect and self-fulfilling prophecy.
Social Variables

16. What is the Rosenthal effect?
For example, teachers might give more attention and feedback to high aptitude students than to low aptitude students.
The Rosenthal effect can confound an experiment, producing results consistent with the experimenter’s expectations.
Social Variables

17. Why is a double-blind design superior to a single-blind design in controlling experimenter bias?
Single-blind experiments only control demand characteristics, since subjects are blinded to their condition.
Double-blind experiments control both demand characteristics and experimenter bias, since both the experimenter and subjects are blinded.
Social Variables

18. How might an experimenter's personality affect experimental results?
Research on experimenter personality shows that when experimenters are warm and friendly, subjects learn more, talk more, earn better test scores, and are eager to please.
Hostile or authoritarian experimenters obtain inferior subject performance.
Personality Variables

19. How can experimenters control personality variables?
Employ multiple experimenters to run an equal number of subjects in each of the experimental conditions (balancing). Treat “experimenter” as an independent variable in statistical analysis. If an interaction is found, then the experiment was confounded.
Personality Variables

20. How can experimenters control personality variables?
When there is a single experimenter, minimize face-to-face contact and closely follow the script. Videotape sessions to confirm consistent performance.
Personality Variables

21. How do volunteers differ from nonvolunteers?
Volunteers are more sociable, score higher in social desirability, hold more liberal social and political attitudes, are less authoritarian, and score higher on intelligence tests than nonvolunteers.
Personality Variables

22. What are context variables?
Context variables are extraneous variables produced by experimental procedures created by the research setting environment, like assignment of participants to conditions.
Context Variables

23. When might subjects select the experiment?
When we allow subjects to sign up for experiments whose titles differ in their appeal: “The Memory Test Experiment” “The Heavy Metal Music Experiment”
However, this could result in a biased sample threatening external validity.
Context Variables

24. Why shouldn’t you run your friends in your experiment?
Selecting your friends might bias your sample, threatening external validity.
Both you and your friends might act differently in your experiment than strangers.
Context Variables

25. Summarize the folklore about subjects.
Subjects who sign up late in the semester may be less motivated and may behave differently than those who sign up earlier in the semester.
Rosenthal speculated that the differences seen at the start and end of an experiment may be just as likely due to changes in the experimenter.
Context Variables