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concern about malpractice suits. On the other hand, without listed reasons from which to choose, physicians may respond as if the survey is a medical board examination and justify their choices on purely clinical grounds when other factors do in fact operate. In addition, surveys cannot uncover defensive practices performed unconsciously by physicians. In short, surveys can elicit responses that are biased in either direction. These obvious problems suggest that it might be better to start with actual behavior as recorded in data on utilization of procedures and try to ascertain the percentage of use that arises from fear of malpractice suits. The only way to measure such a percentage is to relate variations in utilization across physicians to variations in the strength of the “malpractice signal” across physicians. For example, physicians practicing in hospitals or communities with high rates of malpractice claims or high malpractice premiums might be more sensitive to malpractice risks and alter their practices accordingly. Statistical analyses of such variations could pick up these differential effects. To take this tack, data must be available to control for other factors that can account for differences among physicians in their utilization of services, including the health status of the patient population. Often such data are unavailable. Even more troublesome is the fact that this approach can pick up only the incremental effects of stronger versus weaker malpractice signals. It cannot accurately assess the generalized “baseline” level of defensive medicine that may exist in all physicians’ practices. Professional society newsletters and other national media often report on especially large or unusual jury verdicts. Physicians may react to these news items as vigorously as they would to their own or their colleagues experience with malpractice claims. Physicians may be almost as defensive if they face a small risk of being sued as they are if they face a higher risk. This is especially likely if they have the power, with no negative and sometimes positive financial consequences, to order tests and procedures that reduce medical risks to their lowest feasible level. Despite these problems, OTA undertook new analyses that offered the best chance, within time and budgetary constraints, of adding to the current state of knowledge about the scope of defensive medical practice while acknowledging the methodological problems described above. OTA-initiated studies included the following: Four separate physician surveys (conducted jointly with three medical specialty societies) containing hypothetical clinical scenarios that asked respondents to indicate what clinical actions they would take and the reasons for them. The survey materials contained no references to suggest that OTA’s purpose was to study malpractice or defensive medicine, though malpractice concern was one of five reasons listed for each possible course of action. An analysis of the relationship between the use of prenatal care services in low-risk pregnancy and the level of malpractice risk facing doctors in Washington State. An analysis of the relationship between New Jersey physicians’ responses on a clinical scenario survey and their personal malpractice claim history.