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
What is a double-blind study?
Participant and researcher don’t know what groups the participants are in
What is a triple blind study?
Participant and researcher and person scoring the data don’t know the participant groups
What is the placebo effect?
Positive effect simply due to believing you’ve received treatment
What is the nocebo effect?
Negative effect simply due to believing you’ve received treatment
What is the Hawthorne effect?
Behavior changes just because individuals know they are being studied
