1. Physical Variables
Social Variables
Personality Variables
Context Variables

2. Controlling extraneous variables
When we experiment, we want to create treatment conditions that will let us clearly see the effects of the independent variables. We want our experiment to be internally valid, therefore only the independent variable should change from one condition to another.

3. 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

4. Physical variables
A psychologist may test one group of subjects in one room and anther in a different room. In one room, there is a lot of noise from outside. Therefore one group was tested under quiet conditions, the other under noisy conditions. This may affect their performance.

5. 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

6. 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

7. 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.
We have not wiped out the differences between each testing room, but we hope that the effects of the rooms are the same or balanced for both treatment conditions
Physical Variables

8. Example balancing
Let’s say we think that doing yoga will improve people’s moods. Group A does yoga, group B watches a video. Then we test each group by giving them each a mood test. However, group A takes the mood test in a room with a party going on next door and group B takes the mood test in gray quiet room. We find that Group A performs better on the mood test than group B, but what if that is because Group A was listening to a party while they filled out the test. Balancing would let half of group A and half of group B take the mood test in the “party” room and the other half of group A and the other half of group B takes the mood test in the gray room.

9. 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

10. 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

11. Explain demand characteristics.
Demand characteristics are cues within the experimental situation that demand or elicit specific participant responses. Subjects try to act as they feel the researcher wants them to act.
Example: if researcher to tell him when they hear a tone, subjects may say they hear it even if they don’t. They are trying to be good subjects.
Social Variables

12. 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.
Experiment done by Orne & Scheibe (1964) on sensory deprivation
Social Variables

13. What is a single-blind experiment?
One way to control demand characteristics I to do a single blind study. 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

14. 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

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

16. 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. It is used because we want subjects to respond as normally as possible.
They should be used sparingly, since they are a form of deception.
Example: want to see if style of clothing influences confidence levels, but if ask subjects to change into more businesslike attire, they may realize the hypothesis. So make a cover story as to why they should put on the clothes.
Social Variables

17. What is experimenter bias?
Experimenter bias is any behavior by the experimenter that can confound the experiment. Experimenters may not realize it, but they can give subjects cues that tell how the experimenters would like them to respond. Might be warm and friendly in one treatment, more aloof and business-like in another.
For example, an experimenter might provide more attention to subjects in one condition than another.
Social Variables

18. 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.
In these cases, the experimenter is an extraneous variable.
Social Variables

19. 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

20. 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

21. How might an experimenter's personality affect experimental results?
The personal characteristics, or personality variables, that an experimenter brings to the experimental setting can be important.
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

22. Personality variables
Experimenters who themselves score high on social desirability scales are very good at being likeable experimenters. They are more enthusiastic, smile more at subjects, are more friendly. Likeable experimenters collect better data, more useable responses, and fewer “I don’t knows” from respondents.
However, this brings up the question of whether such results from subjects would occur under usual circumstances, or if these super friendly experimenter was the only means of obtaining it.
Advice is to be pleasant, but not overly friendly.

23. 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

24. How do volunteers differ from nonvolunteers?
Do we need to be concerned about the personality variables associated with characteristics of subjects?
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.
Brings into question whether studies using university samples (volunteers) have poorer external validity.
Personality Variables

25. 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 includes subject recruitment, selection, and assignment procedures.
Most common ones include: those occurring when subjects select their own experiments, and those produced when experimenters select their own subjects.
Context Variables

26. When subjects select the experiment
These 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. It is best to keep titles as neutral sounding as possible.
Context Variables

27. 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.
If are standing on corner trying to solicit subjects, don’t only ask those who smile.
Context Variables

28. 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