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This design eliminates the possibility of testing-X interaction.
An experiment in which two or more variables are manipulated.
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 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.
Resembles the one-group pretest-posttest design except multiple observations are made before and after the treatment.
Loss of subjects varies across experimental conditions.
Randomization rules out this threat to internal validity.
May occur when measurement of the dependent variable varies over time or experimental conditions.
A threat to internal validity when a single group is measured at two or more points in time.
Pretests and posttests are administered to experimental conditions but random assignment is not possible.