Of the following experimental designs, the one that is weakest in internal validity is the
A) one-group pretest-posttest design.
B) posttest-only control-group design.
C) pretest-posttest control-group design.
D) time-series design.

Question

Quizplus · Accepted Answer

The one-group pretest-posttest design is weakest in internal validity because it lacks a control group, making it difficult to determine whether changes in the dependent variable are due to the treatment or other external factors.

Of the Following Experimental Designs, the One That Is Weakest