A therapist wants to study the effects of yoga and meditation on stress relief. She has 60 volunteers who experience varying levels of stress. She believes that the volunteers’ professions could have an effect on the results. A preliminary survey reveals that 22 of the volunteers are in high-stress professions. The therapist randomly assigns 11 of these subjects to practice yoga and the remaining 11 to practice meditation. Nineteen of the other 38 volunteers are randomly assigned to practice yoga and the remaining 19 to practice meditation. Before the experiment begins, all the participants will be asked to rate their stress levels on a scale of 0 to 10, with 0 representing "no stress” and 10 representing "highest level of stress.” At the end of one month, the subjects will be asked to rate their stress levels again. The differences in stress levels will be compared for the different stress-relieving activities within the two types of professions.
Which of the following is the best description of the experimental design?
observational study
matched pairs design
randomized block design
completely randomized design