Problem: A researcher is conducting a study to measure how exercise affects mood. The researcher measures the participants' mood before and after 30 minutes of exercise using a self-report questionnaire. Halfway through the study, the researcher changes from the self-report questionnaire to observing participants' behavior and facial expressions as a measurement of mood. The results of the study show that 30 minutes of exercise greatly improves participants' mood. The research study has: Need Assignment Help?