A fourth approach is a statistical method of analyzing patterns of responses that provides two scores. The first is concerned with perception and indicates the patient’s ability to discriminate low levels of the stimulus, a notion akin to estimating the size of “just noticeable” differences. The second score reflects the person’s decision whether to report a stimulus; under conditions of uncertainty, this reflects a personal response bias. This field of analysis derived from the problem of distinguishing signals from background noise in radio and radar, where it is called signal detection analysis. The same analysis may also be applied to other types of decision (e.g., the behavior of baseball players in deciding whether to swing at the ball, or of drivers in deciding when it is safe to merge into traffic) and is here called decision analysis or sensory decision theory. Where it is difficult to judge whether or not a stimulus is present (e.g., whether a radiograph shows a small fracture), two types of error are possible: falsely reporting a fracture, or missing one. Where the radiograph is unclear, the decision is influenced by factors such as the frequency of seeing fractures of this type, clinical conservatism, and the relative importance of avoiding each type of error. The analytic technique uses the notions of “hits” and “false alarms.” A hit occurs where a stimulus is present and I rate it as present; a false alarm occurs where I report a signal that is in fact absent. When it is important to detect a signal, I may set my decision criterion to raise the number.