Observation or experiment? In a study of the relationship between physical fitness and personality, middle-aged college faculty who have volunteered for an exercise program are divided into low-fitness and high-fitness groups on the basis of a physical examination. All subjects then take a personality test. The high-fitness group has a higher average score for "self-confidence."

(a) Is this an observational study or an experiment? Why?

(b) We cannot conclude that higher fitness causes higher self-confidence. Suggest other relationships among these variables and perhaps lurking variables that might explain the higher self-confidence of the high-fitness group.