Lecture 4- Experimental Designs Flashcards
What is an experimental research design?
- Contains one or more factor that is manipulated or controlled (independent variable, IV)
- Contains one or more factor that is measured or observed (dependent variable, DV)
- Ideally, this design establishes that the IV is the cause of the DV
What is a quasi-experiment?
- IV and participants are not randomly assigned
- Weaker evidence for casual conclusions
- Manipulate the IV, but can’t/don’t randomly assign participants to groups or conditions
- More susceptible to threats to internal and external validity
What is a factorial design?
- May include both true and quasi-experimental components
- Consider a true experiment if even 1 IV meets criteria, but strong causal evidence only for the true manipulation
- Multiple IVs examined in 1 design
What is a no-treatment control (posttest only: randomized treatment groups)?
- Participants are randomly put into 2 groups
- Then a treatment (X) or no treatment is applied to both groups
- Then 2 observations are recorded for each group
What is an alternative treatment control (posttest only: randomized treatment groups)?
Similar to no-treatment control, but there are 2 different methods applied to the groups
What is a pretest-posttest: randomized control group design?
- Participants are randomly assigned to 2 groups
- Observation (pretest) before the treatment is introduced
- Then observation following the treatment or no-treatment
What is a solomon randomized four-group design?
Can calculate the impact of test-retest
What is a nonequivalent control group design?
- Compare intact groups (e.g., classrooms)
- Typically pretest-posttest
What are repeated measures?
- AKA within subjects design
- 2 or more measures from the same individual
- May be experimental (e.g., group) or non-experimental (e.g., time)
- Measurements may either occur within a particular session or across multiple sessions
What is counterbalancing?
- Design to avoid order effects
- Randomly assign participants to a given order
What is a single-subject design?
- AKA single case
- Not necessarily conducted on a single participant, but the data are presented in terms of individuals rather than groups
- Repeated measures
- Lacks random assignment
What is a treatment withdrawl design?
AKA reversal design
A1-B-A2
- Applying a treatment and then withdrawing it
What is a treatment reapplication?
A1-B1-A2-B2
- What if the participant doesn’t return to baseline?
What is multiple treatment?
A1-B1-A2-C-A3
- Draw conclusions about B, but note that C always appears after B (serial order confound)
What are multiple baselines?
Observe 2+ behaviors
- One you want to treat first
- One you will treat differently
Across participants:
- Balance treatment orders across more than one individual
- Deals with carryover effects
What is internal validity?
Extent to which conclusions about cause-effect relationships are accurate
How is history a threat to internal validity?
Outside events that influence participants in the course of the experiment or between repeated measures of the DV
How is maturation a 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
How is statistical regression a threat to internal validity?
Participants selected may perform very poorly on a test. However, 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.
How is instrumentation a threat to internal validity?
The reliability of the instrument used to gauge the DV or manipulate the IV may change over the course of an experiment
How is selection a threat to internal validity?
Groups differ in a systematic, non-random way prior to a study
How is mortality a threat to internal validity?
In the course of an experiment, some subjects may drop out before it is completed (attrition).
Particularly problematic if the reason for dropping out is non-random
What is the Rosenthal Effect?
Researcher sets up expectations (intentionally or unintentionally)
What is a single blind study?
Participants don’t know what group they’re in
