Mathematical corrections can be applied to estimate corrected values.84 86 Diagnostic testing is most valuable when the pretest probability of IHD is intermediate for example, when a 50-year-old man has atypical angina, and the probability of IHD is approximately 50% (Table 9). The precise definition of intermediate probability (ie, between 10% and 90%, 20% and 80%, or 30% and 70%) is somewhat arbitrary. In addition to these boundaries, other factors are important in the deci- sion to refer a patient to testing, including the degree of uncertainty acceptable to the physician and patient; the likelihood of an alternative diagnosis; the accuracy of the diagnostic test selected (ie, sensitivity and specificity), test reliability, procedural cost, and the potential risks of further testing; and the benefits and risks of treatment in the absence of additional testing. A definition of 10% and 90%, first advocated in 1980,87 has been applied in several studies.88,89 Although broad, this range still excludes several sizable patient groups (eg, older men with typical angina and younger women with nonanginal pain). When the probability of IHD is high, a positive test result is merely confirmatory, whereas a negative test result might not diminish the probability of disease sufficiently to be clinically useful and could even be misleading because of the possibility that it is a false negative result. When the probability of IHD is very low, however, a negative test result is simply confirmatory, whereas a positive test result might not be clinically useful and could be misleading if falsely positive. 