A threat to internal validity of a study using a two-group pretest-posttest design is that:
A) external events are extremely likely to affect the outcome of these studies.
B) people are more likely to drop out of this type of study.
C) the pretest may sensitize subjects so they change their behavior or responses on the posttest.
D) there is no way to determine if the groups are alike before starting the study.

Question

Quizplus · Accepted Answer

Internal validity is the extent to which the effects detected in the study are a True reflection of reality rather than the result of the effects of extraneous variables. In this example, the fact that subjects have taken the pretest may affect their response to the posttest.
External events are not a threat to the internal validity of this design. Internal validity is the extent to which the effects detected in the study are a True reflection of reality rather than the result of the effects of extraneous variables.
Dropout would depend on the time between the pretest and posttest. Internal validity is the extent to which the effects detected in the study are a True reflection of reality rather than the result of the effects of extraneous variables.
The determination of whether or not two groups are more similar than different is oftentimes the focus of the study. Internal validity is the extent to which the effects detected in the study are a True reflection of reality rather than the result of the effects of extraneous variables.

A Threat to Internal Validity of a Study Using a Two-Group