Module 10: Quasi-Experimental Designs Flashcards
Nonmanipulated independent variable
The independent variable
because participants are not randomly assigned to the two groups. Those groups already exist. Nonmanipulated independent variables are also known as subject (participant) variables.
Single message design
many experimental studies in communication manipulate only 1 message (text, ad, website, newspaper article, etc.)
- Results lead to general conclusions about the effect of the independent variable on the dependent variable.
- Problems with internal validity / construct validity, external validity and reliability
Single-group posttest-only design
A design in which a single group of participants is given a treatment and then tested.
Con: comparisons cannot be made, groups differ too much.
Quasi-experimental design
The term “quasi” (meaning “having some but not all of the features”) preceding the term “experimental” indicates that it resembles an experiment but is not exactly an experiment.
Single-group pretest/posttest design
A design in which a single group of participants takes a pretest, then receives some treatment, and finally takes a posttest
Pro: improvement can be measured
Con: no comparison group that receives no treatment, so you can’t give it to the independent variable
Single-group time-series design
A design in which a single group of participants is measured repeatedly before and after a treatment.
Pro: you can see if the behavior is stable over time and how it changes over time.
Con: statistical regression (or regression to the mean)
Statistical regression (regression to the mean)
threat to internal validity, extreme scores tend to be less extreme when retesting.
Nonequivalent control group posttest-only design
A design in which at least two nonequivalent groups are given a treatment and then a posttest measure.
Con: cannot say indefinitely that the difference is because of the independent variable (the groups might have been unequal at the beginning)
Nonequivalent control group pretest/posttest design
A design in which at least two nonequivalent groups are given a pretest, then a treatment, and finally a posttest.
Pro: a pretest allows assessment
Multiple-group time-series design
A design in which a series of measures are taken on two or more groups both before and after a treatment.
Confounds
Results are always open to alternative explanations, or confounds, uncontrolled extraneous variables or flaws in an experiment
Internal validity
Internal validity is the extent to which the results of an experiment can be attributed to the manipulation of the independent variable rather than to some confounding variable.
