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To the Editor: Dr Welch and colleagues1 reported that patients with acute myocardial infarction (AMI) with initially normal or nonspecific initial electrocardiogram (ECG) results had lower mortality rates than those who presented with diagnostic ECG results. These conclusions are based on odds ratios derived from models comparing mortality in patients with normal or nonspecific ECG results and in patients with ECG signs specific to AMI. Although odds ratios are important measures of association, they do not describe the ability of information—here normal, nonspecific, or specific ECG results—to help the clinician predict the death or survival of a given patient.2 To provide this information, the authors should have focused on the positive and negative predictive values.3 The relevant positive predictive value is the proportion of patients dying in the diagnostic ECG group (11.5%); the relevant negative predictive values would be the proportions of patients surviving in the normal (94.3%) and the nonspecific (91.3%) groups. These predictive values are not impressive.
Furthermore, little information was given on patients who were excluded because they were transferred. Because the decision to transfer might be related to severity, these exclusions could bias the results by increasing or decreasing the overall mortality.4 Because predictive values vary with the frequency of the event predicted, the authors should also have reported the sensitivity and specificity of ECG signs. For instance, the sensitivity of a diagnostic ECG (the proportion of patients who died and who had a diagnostic ECG) and its specificity (the proportion of patients who survived who had a normal or nonspecific ECG) were low—65.1% and 43.9%, respectively.
The poor discriminative power of a diagnostic ECG could be even better summarized by its positive likelihood ratio.5 This measure of gain in information, estimated by dividing the sensitivity by the proportion of false positives, was only 1.16. For a clinician, likelihood ratios are more informative than odds ratios because they compare the odds of dying for a patient with a diagnostic ECG (1.0 to 7.7), to the odds of dying before the results of the ECG are known (estimated, from the overall mortality, at 1.0 to 8.9). The gain in information is small, as predicted from the likelihood ratio close to 1.
It is helpful to clinicians to provide predictive values, sensitivity, specificity, and likelihood ratios when reporting the performance of a diagnostic test.3 Because prognostic studies also analyze problems of prediction, they should systematically report these clinically relevant parameters.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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