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

2. So you want to do an experiment?
You’ve got your theory.
What is the behavior/cognitive process that you want to examine?
What do you think affects that behavior/cognitive process?

3. 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

4. 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.
Now you need to operationalize your variables in terms of how they will be:
Controlled
Manipulated
Measured
Be aware of the underlying assumptions connecting your constructs to your operational variables

5. An example
Hypothesis: Eating candy with peanuts improve memory performance
How might we test this with an experiment?

6. 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
Constants:
M&Ms are eaten
Variables:
Type of M&M: peanut vs plain
Memory performance

7. 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
Peanut candies
Memory
Operational
Peanut M&Ms
Memory test
Underlying assumptions

8. Variables Independent variables (explanatory)
Dependent variables (response)
Extraneous variables
Control variables
Random variables
Confound variables

9. 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

10. 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

11. Choosing your independent variable
Methods of manipulation
Straightforward manipulations
Stimulus manipulation - different conditions use different stimuli
Instructional manipulation – different groups are given different instructions
Staged manipulations
Event manipulation – manipulate characteristics of the context, setting, etc.
Subject manipulations – there are (pre-existing mostly) differences between the subjects in the different conditions (leads to a quasi-experiment)

12. Choosing your independent variable
What about our candy experiment?
1 IV: Candy type (3 levels)
Peanut M&Ms
Plain M&Ms
Bottlecaps

13. Dependent Variables
The variables that are measured by the experimenter
They are “dependent” on the independent variables (if there is a relationship between the IV and DV as the hypothesis predicts).

14. Choosing your dependent variable
How to measure your your construct:
Can the participant provide self-report?
Introspection – specially trained observers of their own thought processes, method fell out of favor in early 1900’s
Rating scales – strongly agree-agree-undecided-disagree-strongly disagree
Is the dependent variable directly observable?
Choice/decision (sometimes timed)
Is the dependent variable indirectly observable?
Physiological measures (e.g. GSR, heart rate)
Behavioral measures (e.g. speed, accuracy)

15. Choosing your dependent variable
What about our candy experiment?
Conceptual level: Memory
Operational level: Some kind of memory test
Memorize a list of words while eating the candy
Then 1 hour after study time, recall the list of words
Measure the accuracy of recall

16. Extraneous Variables Control variables
Holding things constant - Controls for excessive random variability
Number of M&Ms consumed
Time of day test taken

17. Extraneous Variables
Random variables – may freely vary, to spread variability equally across all experimental conditions
Randomization
A procedures that assure that each level of an extraneous variable has an equal chance of occurring in all conditions of observation.
On average, the extraneous variable is not confounded with our manipulated variable.
What your participants ate before the
experiment

18. Control your extraneous variable(s)
Can you keep them constant?
Should you make them random variables?
Two things to watch out for:
Experimenter bias (expectancy effects)
the experimenter may influence the results (intentionally and unintentionally)
E.g., Clever Hans
One solution is to keep the experimenter “blind” as to what conditions are being tested
Demand characteristics – cues that allow the participants to figure out what the experiment is about, influencing how they behave

19. Confound Variables Confound variables
Other variables, that haven’t been accounted for (manipulated, measured, randomized, controlled) that can impact changes in the dependent variable(s)

20. Next time Read chapters 4 & 5.
Bring your textbook and/or APA Publication Manual to lab (if you’ve got one)
Don’t forget your first journal summary is due this week in lab

21. Exam Average = 81.8
Range: