Final Exam Flashcards
Experiment
Must include at least one manipulated variable and at least one measured variable
Manipulated Variable
Researcher assigns participants to levels of the variable
Measured Variable
Researcher records what happens
Independent Variable
Manipulated Variable
Dependent Variable
Measured Variable
Control Variable
Any variable that an experimenter holds constant
Why do an experiment?
To have a more valid study, to make causal claims, to generalize more people, to collect evidence in the real world, to be the most scientific
What types of groups are used in experiments?
Treatment Groups, Comparison Groups, Control Groups, Placebo Group
How do experiments apply to covariance, temporal precedence, and internal validity?
It is also about the outcome, the cause variable comes before the effect variable, and well designed experiments rule out alternative explanations
Design Confound
When a second variable varies systematically along with the IV
Systematic Variability
Design Confound
Unsystematic Variability
Randomly distributed across groups
Selection Effect
Participants in one level of the IV are systematically different than participants in the other level of the IV
How do you avoid selection effects?
Random Assignment and Matched Groups
Independent Groups Designs
Different groups of participants are placed at different levels of the IV
Within-Groups Design
Each participant is presented with all levels of the IV
Posttest Only Design
Participants are randomly assigned to IV groups and are tested on the DV just once
Pretest/Posttest Design
Participants are tested on the DV once before and once after exposure to the IV
What can obscure the differences between means?
Too much variability within-groups
What are the sources of unsystematic variability?
Measurement Error, Individual Differences, and Situation Noise
Factorial Designs
A study with two independent variables
What can factorial designs do?
Test limits, test theories, and show interactions
IVs can be manipulated as:
Within-groups or Between-groups
What would the method section of an empirical journal article state?
This was a factorial design with ____ and ____ as independent variables.
What will the results section describe?
The statistical tests for main effects and interactions
What should be looked for in popular press articles?
Key phrases such as “it depends”
Concurrent Measures Design
Participants are exposed to all levels of the IV at the same time and preference is the DV
Repeated Measures Design
P’s are measured on the DV after exposure to each level of the IV
What are the advantages of within-groups designs?
Equivalent Groups, increases power to detect difference between conditions, requires fewer participants
Equivalent Groups
Participants serve as their own controls
What are the disadvantages of within-groups designs?
Order Effect, Might not be practical or possible, Demand Characteristics
Order Effect
Being exposed to one condition may change how participants respond to other conditions
Counterbalancing
Presenting levels of the IV to participants in different orders
Manipulation Check
An extra DV is added to quantify how well a manipulation worked
Pilot Study
Uses a separate group of P’s to confirm the effectiveness of the IV manipulation
What is known as the really bad experiment?
One group pretest/posttest design
What are the Dirty Dozen Threats to Internal Validity?
Design confound, selection effect, order effect, maturation, history, regression to the mean, attrition, testing, instrumentation, observer bias, demand characteristics, placebo effects
Maturation Threat
A spontaneous change in behavior over time
History Threat
Some external event affects most members of the treatment group at the time of the treatment
Regression Threat
Extremely low or high scores at time 1 are less likely to be extreme at time 2
Attrition Threat
Some participants drop out of the study from pretest to posttest
Testing Threat
A change in participants as a result of experiencing the DV more than once
Instrumentation Threat
Occur when the measuring instrument changes over time
How would you describe the main effect?
“There is a main effect for _____ such that _____ is higher than _____.
How would you describe an interaction?
Every interaction is different - there is no single sentence structure
Try the simple main effects strategy
