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May occur when measurement of the dependent variable varies over time or experimental conditions.
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.
Pretests and posttests are administered to experimental conditions but random assignment is not possible.
Controls for the effects of history in a trend analysis by comparing a group exposed to the treatment with other groups that are not.
Loss of subjects varies across experimental conditions.
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.
This design eliminates the possibility of testing-X interaction.
An experiment in which two or more variables are manipulated.
A potential threat to validity when subjects are selected on the basis of their extreme scores on the dependent variable.
A matter of how well an experiment controls for the effects of extraneous variables.