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May be confounded with the independent variable when a single group is studied over an extended period of time.
Randomization rules out this threat to internal validity.
Controls for the effects of history in a trend analysis by comparing a group exposed to the treatment with other groups that are not.
An experiment in which two or more variables are manipulated.
Selection and differential attribution are the primary threats to internal validity of this design.
The effect of X on Y depends on Z.
Resembles the one-group pretest-posttest design except multiple observations are made before and after the treatment.
Loss of subjects varies across experimental conditions.
Pretests and posttests are administered to experimental conditions but random assignment is not possible.
May occur when measurement of the dependent variable varies over time or experimental conditions.
This design eliminates the possibility of testing-X interaction.
A matter of how well an experiment controls for the effects of extraneous variables.