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