number of services than would be the optimal amount for the patient in order to increase revenue. Some of the proposed healthcare models in the Patient Protection and Affordable Care Act (PPACA) could modify how a physician is reimbursed for delivering care that would reward quality over quantity thereby reducing SID. One of these models, the Accountable care organization (ACO), reimburses a physician through a gain-sharing model that encourages them to collaborate with other providers to deliver care thus removing some of the individual incentives to induce demand. Pay for performance may also provide a strategy to discourage overuse of unnecessary, low-value interventions by reimbursing for quality of care delivered. Professional uncertainty hypothesis The professional uncertainty hypothesis suggests that due to autonomy and individual practice patterns, physicians differ in their opinions regarding the effectiveness, appropriateness, and success rates of various treatment options for a particular condition. This leads to a level of uncertainty which may result in a lack of uniformly acceptable standards of care that can be followed by all physicians. This uncertainty may lead to different levels of recommended consumption (demand) to patients for healthcare services. The use of evidence-based guidelines based on scientific evidence of improved outcomes for the diagnosis and treatment of a particular condition may reduce some physician autonomy but have a greater impact in reducing the professional uncertainty that may lead to SID. Variations in care and SID It is unclear the extent to which SID explains geographic variations in care. It is a complicated topic. It is difficult to know how much is done explicitly to raise a physician's income and how much is practice style or professional uncertainty. Physicians who are more entrepreneurial may be interested in maximizing income. Surgeons may have more opportunity to manipulate demand. They may be more enthusiastic about certain procedures they perform because they generate more revenue or because they value the surgical treatment. Overutilization The simple adage, "if you build it they will come," applies to SID and the medical profession. It appears when resources are available, overutilization occurs even when improved quality and outcomes are uncertain. This occurs daily in hospital intensive care units, at primary care physician offices and with overutilization of expensive radiologic technology and laboratory testing. "Research suggests that those who invest in imaging equipment order more CT and MRI tests than doctors who haven't made the investment." Analysts report that physicians