After only 2 minutes on the treadmill, each participant was given the option to stop the experiment. This brief time interval was chosen so that participants were given the option to stop before any...

After only 2 minutes on the treadmill, each participant was given the option to stop the experiment. This brief time interval was chosen so that participants were given the option to stop before any of them could reasonably be expected to be experiencing fatigue. Data for the participants who decided to stop after only 2 minutes were not included in the analysis of the final results. Fifteen students chose to stop in the concentration group; 10 stopped in the music group; and no students stopped in the video group. The results did not support the researcher’s predictions. The mean strenuousness score (on a scale from 0 to 100) for students who completed the experiment was highest for the concentration group (70), next highest for the music group (60), and lowest for the video group (50).

A Identify a possible threat to the internal validity of this experiment, and explain how this problem could account for the unexpected results of the study.

B Assume that a pretest measure was available for each of the 120 participants and that the pretest measured the degree to which each subject was likely to persist at exercise. Describe how you could use these pretest scores to confirm that the problem you identified in question 2A had occurred.