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