What is a quasi-experiment, and how does it differ from a true experiment?
It lacks random assignment but still examines cause-and-effect relationships
Why do quasi-experiments typically have lower internal validity than true experiments?
They lack random assignment
What is a nonequivalent control group design?
A design comparing two groups that were not randomly assigned
What is the difference between a posttest-only design and a pretest/posttest design in quasi-experiments?
One includes a measurement before the treatment and the other does not
Why is it difficult to establish causation in quasi-experiments?
They lack internal validity due to possible confounds
What is the primary factor that distinguishes a quasi-experiment from a “true” experiment?
Researchers in a quasi-experiment lack full experimental control over the independent variable.
A study compared organ donation rates between countries with “opt-in” policies and those with “opt-out” (presumed consent) policies. Because the researchers could not randomly assign people to live in these countries, this is an example of a:
Nonequivalent control group posttest-only design.
Which internal validity threat occurs when the participants in one level of the independent variable are systematically different from those in the other level at the start of the study?
selection effect
Which of the following is often used as a synonym for “quasi-experiment” because the independent variable is manipulated by outside forces rather than the researcher?
Natural experiment
What does internal validity refer to in a research study?
determines there is a cause-and-effect relationship between variables
What is true about case studies?
They involve an in-depth analysis of one person, group, or event.
What is a quasi-independent variable?
A preexisting characteristic that differentiates groups in a study
What are some examples of quasi-independent variables?
IQ scores between smokers and non-smokers
What is the primary factor that distinguishes a quasi-experiment from a true experiment?
The lack of full experimental control over the independent variable.
A researcher studies the impact of a new state law by measuring a variable repeatedly before and after the law is enacted. What is this design called?
Interrupted time-series design
What is the definition of random assignment?
making multiple equivalent groups out of participants with similar characteristics
The results of a self-esteem survey on two groups, one that got plastic surgery and another that didn’t, resulted in a graph with two lines that diverge. What does this spreading interaction indicate?
there is an effect on self esteem in one group, but a weak or no effect on the other
A quasi-experimental design was completed, and participants in each group were measured for depressive symptoms before, and once a week for 3 months after being administered a new drug. What type of design is this?
interrupted time-series design with nonequivalent groups
When does a ‘design confound’ become a problem in certain quasi-experiments?
When some external variable systematically co-varies with the independent variable.
When does ‘observer bias’ become an internal validity threat in an experiment?
When the experimenters’ expectations influence their interpretation of the results.
In a quasi-experiment, what term is used for the variable that the researchers do not have full experimental control over?
The quasi-independent variable
Why might ethical concerns lead researchers to choose a quasi-experimental design?
It is unethical to randomly assign participants to potentially harmful treatments.
A researcher studies the effects of a new school policy by comparing test scores from this year’s students to last year’s students. What is the main concern with this design?
It may include a history threat
In a quasi-experiment, which type of variable represents a preexisting difference between groups?
Quasi-independent variable
