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Resembles the one-group pretest-posttest design except multiple observations are made before and after the treatment.
A potential threat to validity when subjects are selected on the basis of their extreme scores on the dependent variable.
A threat to internal validity when a single group is measured at two or more points in 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.
Pretests and posttests are administered to experimental conditions but random assignment is not possible.
Selection and differential attribution are the primary threats to internal validity of this design.
An experiment in which two or more variables are manipulated.
May be confounded with the independent variable when a single group is studied over an extended period of time.
May occur when measurement of the dependent variable varies over time or experimental conditions.
Loss of subjects varies across experimental conditions.
Randomization rules out this threat to internal validity.