Experimental Design Flashcards
What are treatments?
-Levels of an IV
What is required of a true experiment?
- IV AND random assignment
- Allows for strong evidence for causal conclusions
What is a quasi-experiment?
- Manipulate IV but no random assignment of participants or conditions (i.e. intact groups)
- Weaker evidence for causal conclusions
- More susceptible to threats to internal and external validity
What is a factorial design?
- Multiple IV’s examined in one design
- Examines main effects and interactions (i.e. 2 X 3 design)
- May include both true and quasi-experimental components
What is an advantage of the factorial design?
-Can examine effects of IV on participants (main effects) and how 2+ IV interact with one another (interaction)
What are disadvantages of the factorial design?
- Requires a relatively large number of participants
- Becomes very complex with each additional IV
Describe the multiple baseline design.
- Can be established across 2+ observed behaviors
- Can be established across participants
What are levels of evidence based on?
1) Strength of the evidence: how well you can draw causal conclusions
2) Depth: amount of converging evidence
What is internal validity?
- Extent to which conclusions about cause-effect relationships are accurate
- Might there be other explanations (covert variables) for the observed patterns
What are the threats to internal validity?
- History
- Maturation
- Statistical regression
- Instrumentation
- Selection
- Mortality
- Experimenter/participant bias
Describe the history threat to internal validity.
-Outside events that influence participants in the course of the experiment or between repeated measures of the DV
Describe maturation threat to internal validity.
- Participants may change in the course of the experiment or between repeated measures of the DV due to the passage of time
- EX permanent change: biological growth
- EX temporary change: fatigue
Describe statistical regression (regression to the mean) threat to internal validity.
- Participants with extreme scores on a first measure of the DV tend to have scores closer to the mean on a second measure
- Extreme scores are more likely to occur via chance
- Highlights the important of control group
Describe instrumentation threat to internal validity.
- The reliability of the instrument sued to gauge the DV or manipulate the IV may change over the course of an experiment
- EX: changes in equipment calibration, changes in proficiency of “human” instruments
- Possible in any pretest-posttest design
- Importance of recruiting study groups in parallel
Describe selection threat to internal validity.
- Groups differ in a systematic, non-random way prior to a study (i.e. intact groups)
- Only weaker cause-effect conclusions are possible
- May co-occur with maturation differences (i.e. different learning rate prior to the study) and/or history differences (i.e. differences in teacher style in 2 classrooms)
