1. Basics of Experimentation
Ryan M. Denney, Ph.D
The University of Southern Mississippi
PSY 361

2. Variable Definition Recap
Any characteristic of the organism, environment, or experimental situation that can vary, adjust, or change
An event, experience, or behavior that can assume at least two values

3. Independent Variable (IV)
The factor that is the major focus of the research and that the researcher directly, purposely manipulates.
Independent – can be directly manipulated by the investigator
Variable – must assume two or more values (levels)
The causal part of the relation we seek to establish.
Ex: Drug dosage, time spent in tutoring, social skills training

4. Types of Independent Variables
Physiological IV
The physiological state of the participant that the experimenter manipulates (ex. Intoxication level, sexual arousal, central nervous system arousal through violent scenes)
Experience IV
The amount or type of training/learning is manipulated (ex. Cognitive therapy, puzzle completion, training in diagnostic interviewing)
Stimulus or environmental IV
An aspect of the environment that the experimenter manipulates (ex. Noise level, lighting, number of people observing, electric shock)

5. Dependent Variable (DV)
A response or behavior that is measured.
The variable that is measured
Is the “effect” half of the cause-and-effect relation we are examining
It is hoped that changes in the DV are directly related to manipulation of the IV (cause)
Ex: Depression level, academic performance, meaning in life, hopefulness, marital contentment, job satisfaction
Any variable we want to impact (or on which we wish to measure the impact of an IV)

6. Recording/Measuring the DV
Correctness
Only correct responses are counted
Ex: Number of correct answers on a math test
Rate
Rate of responding determines how rapidly responses are made during a specified time period (ex: the time between response 1 and response 2)
Ex: How fast a lever was pulled in a 3 minute period, number of eye saccades /1 min
Frequency
The number of responses or events that occur within a specified time
Ex: The number of times the lever was pulled in a 3 minute period
Degree or Amount
How much of an attribute is reported
Ex. Score on a measure of life satisfaction, degree of optimism about the future
Latency and Duration
Latency: How quickly participants make an initial (first) response; Ex: how fast sprinter starts at gun (reaction time)
Duration: How long the response lasts; Ex: duration of cooing or crying in infants

7. Extraneous Variables and Confounds
Extraneous Variables: Uncontrolled variables that can cause unintended changes in the DV or between groups
Variables that systematically vary along with the IV.
Confound: The results of an experiment can be attributed to either the operation of an IV OR an extraneous variable
Ex. Testing the effect of caffeine on alertness. We give a group of participants a caffeine pill at noon and test their alertness. We give another group of participants a placebo at midnight and test their alertness. What is the confound?
Ex: Relationship between academic satisfaction and optimism about the future. Confounding variables?

8. Psychological Experiments
The goal of an experiment is to establish a cause-and-effect relationship between two variables
Demonstrate that changes in one variable (IV) are directly responsible for (causes) changes in a second variable (DV)
Necessary elements:
Manipulation of IV and measurement of DV
Control of EVs
Psychological Research involves experiments, but not all psychological research is “experimental”

9. Types of Experimental Hypotheses
Directional Hypothesis: the outcome of the experiment is specified/predicted
Greater chances of finding a statistically significant result
Ex: Students receiving visual stimulus + live interactive instruction (Group A) will perform better on a measure of academic ability than students in who receive visual stimulus- only instruction (classroom vs. online learning)
(Group B).
Nondirectional Hypothesis: Does not predict the exact direction of the experiment’s outcome
Ex: Children who attend private schools (Group A) will differ from children who attend public schools (Group B) on a measure of playground anxiety

10. Construct an Experiment
1. Hypothesis
One variable that may cause change in another variable
2. Independent variable
3. Dependent variable
4. Potential extraneous variables

11. Example Experiment Sleep and memory IV: Minutes of Sleep
DV: Number of words of a story that are recalled
EV: Motivation, reading ability, verbal ability, physiological/sleep need differences

12. Example Experiment Caffeine and startle response
IV: Amount of Caffeine
DV: number of times participants visibly startles at a random loud noise
EV: Temperament; physiological differences in: tolerance, metabolization, and startle respons; previous experiences with startling noises.