Exam 3 Flashcards
Quasi-Experiments
Independent variable is manipulated despite no random assignment, groups aren’t equivalent
- Practical/ethical reasons
- Must carefully monitor threats to internal validity
- Could yield meaningful results even w/ no causation established
Pre-Experimental Designs
Data collected in a way that offers multiple explanations for data
Types of Pre-Experimental Designs
- One Shot Study
- Pretest/Posttest (one group)
- Nonequivalent control group
One-Shot Study
One group of participants is tested
- Disadvantage: How do we know if there was any change?
- Example: count drug-related deaths after a rehab program is implemented
Nonequivalent Control Group
An experimental and nonequivalent control group are tested once
- Disadvantage: may already be significant differences between groups
- Example: count drug-related deaths in this and another city after implementing rehab program
Pretest/Posttest
One group of participants is tested at pretest and posttest
- Disadvantage: Something else could have happened between the two testings
- Example: compare drug-related deaths before and after a rehab program is implemented
Types of Quasi-Experiments
- Pretest-Posttest Nonequivalent Control Group
- Time-Series Design
- Multiple Time-Series Design
Pretest-Posttest Nonequivalent Control Group
Two comparable but not randomly assigned groups of participants are tested before and after treatment
- Allows you to measure relative change between two groups
Time-Series Designs
One group is tested several times before and several times after treatment
- If data show a consistent trend, the likelihood that results are due to a confounding variable is reduced
Multiple Time-Series Design
Two nonequivalent groups are tested several times before and several times after treatment
- Can observe change in experimental group before and after manipulation
- Can measure relative change between both groups when independent variable manipulation is introduced
- Essentially a combo of time-series design and nonequivalent control groups design
Threats to Internal Validity of Quasi-Experimental Designs
- When multiple measures are made
- Statistical Regression
- Subject Attrition (Mortality)
- Selection Bias
- Interactions of selection with other threats to internal validity
When Multiple Measures are Made (Threats to Internal Validity in Quasi-Experiments)
Can lead to history, maturation, testing, and instrumentation effects
- Can be controlled by assessing/accounting for issues
Statistical Regression (Threats to Internal Validity in Quasi-Experiments)
Extreme scores are likely to move toward the mean upon retesting
- Can be avoided by not choosing participants on the basis of extreme scores
Subject Attrition/Subject Mortality (Threats to Internal Validity in Quasi-Experiments)
Loss of participants’ data either due to participants withdrawing from study OR because a decision was made to drop their data due to criteria
- Threat when dropout rate is very high or when dropout rate varies between groups
- Bigger problem with nonequivalent groups
Selection Bias (Threats to Internal Validity in Quasi-Experiments)
Differences between the comparison groups within a study
- Sometimes no better alternative
- Example: if someone had sleep apnea it would be hard to access enough patients to assign some to a no-treatment group, so recruit family/friends
Interactions of Selection with Other Threats to Internal Validity (Threats to Internal Validity in Quasi-Experiments)
Occurs when extraneous variables effect one group, but not the other
- Selection can also interact with extraneous variables like maturation, instrumentation, and regression towards the mean
Factorial Designs
The effect of a dependent variable of two or more independent variables is assessed simultaneously
- Can save on time and participants
Factor (Factorial Design)
Another name for independent or subject variables in the design
- Equal to number of main effects
- Marginal means
Levels of Factors (Factorial Design)
Different levels of each factor (would be conditions in non-factorial design)
Unique Condition (Factorial Design)
Unique combination of factors
- equal to levels of all factors multiplied
Types of Factorial Designs
- Within-Groups Design
- Between-Groups Design
- Mixed Design
Higher Order Design
3 or more factors
Within-Groups Design (Factorial Design)
All participants experience all levels/combos of all factors
Advantages: saves time, lower error variance, less participants
Disadvantages: carryover effects, can’t test subject variable