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A threat to internal validity when a single group is measured at two or more points in time.
Randomization rules out this threat to internal validity.
An experiment in which two or more variables are manipulated.
Loss of subjects varies across 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.
This design eliminates the possibility of testing-X interaction.
A potential threat to validity when subjects are selected on the basis of their extreme scores on the dependent variable.
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.
A matter of how well an experiment controls for the effects of extraneous variables.
May occur when measurement of the dependent variable varies over time or experimental conditions.
May be confounded with the independent variable when a single group is studied over an extended period of time.