Experimental Research
Experiment
Study in which IV is manipulated & DV is measured while extraneous variables are controlled.
Internal Validity vs. External Validity
I: carefully controlled to rule out all possible alt explanations.
E: designed to apply in real world situations
Between-subjects experiment:
Each participant is assigned to one condition.
Carryover effect
When being tested in one condition changes behavior in later conditions.
How do researchers deal with carryover effects?
They use counterbalancing, which varies the order of conditions across participants.
Covariance, Temporal Precedence, Extraneous Variable: give experiment what?
Gives experiments CAUSATION.
Manipulation
Carefully changing level of the IV across group/situation.
3 Types of Control Groups
Placebo: A treatment that looks real but has no active ingredient.
Placebo effect: When participants improve just because they believe they received a treatment.
No-treatment control condition: A control group that gets no treatment at all, not even a placebo.
Practice effect, Fatigue effect, Context effect
What are advantages of a between-subjects design?
- Conceptually simpler
- Less testing time per participant
- No carryover effects (no need for counterbalancing)
Covariance
Relationship between two variables where they change together.
Condition
One level of the IV in an experiment.
Within-subjects experiment
An experiment where each participant is tested in all conditions.
Practice effect
Participants perform better in later conditions because they’ve had practice.
Pilot test
A small, trial run of a study to make sure the procedure works as planned.
Temporal Precedence
Variable A (IV) needs to come before variable B (DV).
Confounds
Extraneous variable that distorts the relationship between IV & DV.
Main advantage of a within-subjects experiment?
It removes noise because the same people are in every condition (groups are identical, eliminating individual differences).
Participants perform worse in later conditions because they’re tired or bored.
Experimenter expectancy effect
When the researcher’s expectations influence participants’ behavior.
Extraneous Variables
Any variable (not the IV) that can potentially affect dependent variable in study.
Random assignment
Main disadvantage of a within-subjects experiment?
Participants may change over time, leading to carryover effects.
Context effect
Behavior changes because of the context or order in which responses are made.