Which of the following types of subject loss poses the most serious threat to internal validity?
When participants begin an experiment but fail to complete it, the internal validity of the experiment can be threatened. Which of the following types of subject loss poses the most serious threat to internal validity?
A. the loss occurs because of an error by the experimenter.
B. the loss leads to different numbers of participants in the groups in the experiment.
C. the loss occurs because of equipment failure.
D. the loss occurs because of some characteristic of the participant that is related to the outcome of the study.