Figure 1.

Decision tree for choice of treatment in case of suspected myocardial infarction (MI) of aspirin only v aspirin and streptokinase v aspirin and tissue plasminogen activator. P stands for probability. For example, P2a is the probability of surviving without impairment for someone who has had an MI and who has been treated with aspirin only. The formulas for expected utilities are aspirin, P1{(1*P2a) + (0*P3a) + (0.5*P4a) + (0*P5a) + (0*P6a)} + (1−P1){(1*P7a) + (0*P8a) + (0.5*P9a) + (0*P10a) + (0*P11a)}; streptokinase, P1{(1*P2b) + (0*P3b) + (0.5*P4b) + (0*P5b) + (0*P6b)} + (1−P1){(1*P7b) + (0*P8b) + (0.5*P9b) + (0*P10b) + (0*P11b)}; tissue plasminogen activator, P1{(1*P2c) + (0*P3c) + (0.5*P4c) + (0*P5c) + (0*P6c)} + (1−P1){(1*P7c) + (0*P8c) + (0.5*P9c) + (0*P10c) + (0*P11c)}. Figures on the far right are values