1. Experiment Basics: Variables
Psych 231: Research Methods in Psychology

2. Exam 1 Results My apologies, I didn’t finish grading them yet.
Mean: ??%
Median: ??%
Range: ??
My apologies, I didn’t finish grading them yet.
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If you want to go over your exam set up a time to see me
Exam 1

3. Print out the Class experiment exercise (from the Lab web page) and bring it to labs this week
Turn in your data sheets (pass to front)
I will analyze the data and the results will be discussed in labs this week
Turn in your consent forms
Class Experiment

4. So you want to do an experiment?
You’ve got your theory.
What behavior you want to examine
Identified what things (variables) you think affects that behavior
So you want to do an experiment?

5. So you want to do an experiment?
You’ve got your theory.
Next you need to derive predictions from the theory.
These should be stated as hypotheses.
In terms of conceptual variables or constructs
Conceptual variables are abstract theoretical entities
Consider our class experiment
Theory & Hypotheses:
What you try to memorize & how you try to memorize it will impact memory performance.
Concrete vs. abstract things
Depth of processing
Recall of things from memory
So you want to do an experiment?

6. So you want to do an experiment?
You’ve got your theory.
Next you need to derive predictions from the theory.
Now you need to design the experiment.
You need to operationalize your variables in terms of how they will be:
Manipulated
Measured
Controlled
Be aware of the underlying assumptions connecting your constructs to your operational variables
Be prepared to justify all of your choices
So you want to do an experiment?

7. Constants vs. Variables
Characteristics of the psychological situations
Constants: have the same value for all individuals in the situation
Variables: have potentially different values for each individual in the situation
Variables in our experiment:
Levels of processing
Type of words
Memory performance
Time for recall
Kind of filler task given
Pacing of reading the words on the list …
Constants vs. Variables

8. Variables Conceptual vs. Operational
Conceptual variables (constructs) are abstract theoretical entities
Operational variables are defined in terms within the experiment. They are concrete so that they can be measured or manipulated
Conceptual
How we memorize
(Levels of processing)
Kinds of things
Memory
Operational
Has an ‘a’
‘Related to ISU’
Words rated as abstract or concrete
Memory test
Variables

9. Many kinds of Variables
Independent variables (explanatory)
Dependent variables (response)
Extraneous variables
Control variables
Random variables
Confound variables
Correlational designs
have similar functions
Many kinds of Variables

10. Many kinds of Variables
Independent variables (explanatory)
Dependent variables (response)
Extraneous variables
Control variables
Random variables
Confound variables
Many kinds of Variables

11. Independent Variables
The variables that are manipulated by the experimenter (sometimes called factors)
Each IV must have at least two levels
Remember the point of an experiment is comparison
Combination of all the levels of all of the IVs results in the different conditions in an experiment
Independent Variables

12. Independent Variables
Condition 1
Condition 2
Factor A
1 factor, 2 levels
Cond 1
Factor A
Cond 3
Cond 2
1 factor, 3 levels
Cond 1
Factor B
Cond 3
Cond 2
Factor A
Cond 4
Cond 6
Cond 5
2 factors, 2 x 3 levels
Independent Variables

13. Manipulating your independent variable
Methods of manipulation
Straightforward
Stimulus manipulation - different conditions use different stimuli
Instructional manipulation – different groups are given different instructions
Staged
Event manipulation – manipulate characteristics of the context, setting, etc.
Subject (Participant)– there are (pre-existing mostly) differences between the subjects in the different conditions
leads to a quasi-experiment
Abstract vs. concrete words
Has an “a” vs. “ISU related”
Manipulating your independent variable

14. Choosing your independent variable
Choosing the right levels of your independent variable
Review the literature
Do a pilot experiment
Consider the costs, your resources, your limitations
Be realistic
Pick levels found in the “real world”
Pay attention to the range of the levels
Pick a large enough range to show the effect
Aim for the middle of the range
Choosing your independent variable

15. Identifying potential problems
These are things that you want to try to avoid by careful selection of the levels of your IV (may be issues for your DV as well).
Demand characteristics
Experimenter bias
Reactivity
Floor and ceiling effects
Identifying potential problems

16. Demand characteristics
Characteristics of the study that may give away the purpose of the experiment
May influence how the participants behave in the study
Examples:
Experiment title: The effects of horror movies on mood
Obvious manipulation: Having participants see lists of words and pictures and then later testing to see if pictures or words are remembered better
Biased or leading questions: Don’t you think it’s bad to murder unborn children?
Demand characteristics

17. Experimenter Bias Experimenter bias (expectancy effects)
The experimenter may influence the results (intentionally and unintentionally)
E.g., Clever Hans
One solution is to keep the experimenter (as well as the participants) “blind” as to what conditions are being tested
Experimenter Bias

18. Reactivity Knowing that you are being measured
Just being in an experimental setting, people don’t always respond the way that they “normally” would.
Cooperative
Defensive
Non-cooperative
Cooperative
“You seem like a nice person: I’ll help you get the right results”
Defensive
“I don’t want to look stupid/evil. I’ll do what a smart/good person is expected to do (rather than what I normally would do).”
Noncooperative
“This experiment is annoying. Let me screw up the results.”
Reactivity

19. Floor effects A value below which a response cannot be made
As a result the effects of your IV (if there are indeed any) can’t be seen.
Imagine a task that is so difficult, that none of your participants can do it.
Floor effects

20. When the dependent variable reaches a level that cannot be exceeded
So while there may be an effect of the IV, that effect can’t be seen because everybody has “maxed out”
Imagine a task that is so easy, that everybody scores a 100%
To avoid floor and ceiling effects you want to pick levels of your IV that result in middle level performance in your DV
Ceiling effects

21. Range effects Floor: A value below which a response cannot be made
As a result the effects of your IV (if there are indeed any) can’t be seen.
Imagine a task that is so difficult, that none of your participants can do it.
Ceiling: When the dependent variable reaches a level that cannot be exceeded
So while there may be an effect of the IV, that effect can’t be seen because everybody has “maxed out”
Imagine a task that is so easy, that everybody scores a 100%
To avoid floor and ceiling effects you want to pick levels of your IV that result in middle level performance in your DV
Range effects