The basic purpose of a decision model is to estimate the prognosis of a patient or a population of patients subsequent to each alternative choice of management strategy being compared. For practical reasons, the analysis must be restricted to a time frame, often referred to as the time horizon of the analysis. The time horizon may be finite (e.g., 5 years from the time of decision) or may be indefinite or defined in operational terms such as “for the remainder of the patient's life” or “until all patients in the population are dead.” The choice of time horizon is determined by many factors, including the time frame of events of interest, the availability of data, and the perspective of the analysis. When the time horizon ...