You are in charge of marketing your company’s laboratory services to managed care plans in your region. Contrast approaches to promoting these products to a PPO and to a staff model HMO. You are a territory manager for the cardiology division of a major medical device company. You notice that among the five largest cardiology groups in your area there is a threefold difference between lowest and highest use of your penetrated market. Using what you know about local area variations and physician behavior, what might explain this difference?