A researcher conducted a series of experiments on the effects of external factors that might influence people’s persistence in exercise programs. In one of these experiments, the researcher...

A researcher conducted a series of experiments on the effects of external factors that might influence people’s persistence in exercise programs. In one of these experiments, the researcher manipulated three types of distraction while participants walked on a treadmill. The three types of distraction were concentrating on one’s own thoughts (concentration group), listening to a tape of music (music group), and watching a video of people engaging in outdoor recreation (video group). The dependent variable was how strenuous the treadmill exercise was at the time the participant decided to end the session (the incline of the treadmill was regularly increased as the person went through the session, thereby making the exercise increasingly strenuous). In an introductory psychology course, 120 students volunteered to participate in the experiment, and the researcher randomly assigned 40 students to each of the three levels of the distraction variable. The researcher expected that the mean strenuousness score would be highest in the video group, next highest in the music group, and lowest in the concentration group.