The expected value of information of differential diagnostic tools. The EVI of DDX tools is based on the monetarized value of the morbidity and mortality prevented by promptly establishing a particular diagnosis, multiplied by the probability of that diagnosis, minus costs and monetarized value of time and complications from diagnostic tests that modify the probability of that diagnosis. The prior diagnostic possibilities (left column) are updated by diagnostic tests to produce updated diagnostic probabilities (right column). The updating here increases the likelihood of those diagnoses with greater preventable morbidity and mortality, therefore increasing EVI. However, the updating could proceed in the opposite direction, increasing the likelihood of diagnoses with lesser preventable morbidity and mortality, therefore, decreasing EVI. Costs associated with the diagnostic tests lower EVI (shown here by the red arrows). An optimal DDX decision support tool could be viewed as that which maximizes EVI. EVI: expected value of information.