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Randomization rules out this threat to internal validity.
Pretests and posttests are administered to experimental conditions but random assignment is not possible.
A threat to internal validity when a single group is measured at two or more points in time.
Loss of subjects varies across experimental conditions.
A potential threat to validity when subjects are selected on the basis of their extreme scores on the dependent variable.
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.
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.
Selection and differential attribution are the primary threats to internal validity of this design.
This design eliminates the possibility of testing-X interaction.
May occur when measurement of the dependent variable varies over time or experimental conditions.