.png){kind=icon}
Randomization rules out this threat to internal validity.
May occur when measurement of the dependent variable varies over time or experimental conditions.
This design eliminates the possibility of testing-X interaction.
Loss of subjects varies across experimental conditions.
May be confounded with the independent variable when a single group is studied over an extended period of time.
The effect of X on Y depends on Z.
Controls for the effects of history in a trend analysis by comparing a group exposed to the treatment with other groups that are not.
A matter of how well an experiment controls for the effects of extraneous variables.
A threat to internal validity when a single group is measured at two or more points in time.
An experiment in which two or more variables are manipulated.
Pretests and posttests are administered to experimental conditions but random assignment is not possible.
Resembles the one-group pretest-posttest design except multiple observations are made before and after the treatment.