Management Sensitivity and Specificity
The means and variances of the sensitivity and specificity and the mean of the PVP of the management decisions with respect to the independent gold standard are summarized in Table 3. Level 1 refers to the analog images, level 2 to the uncompressed digital, and levels 3, 4, and 5 refer to those images where the breast section was compressed to 0.15, 0.4 and 1.75bpp respectively (and where the label was compressed to 0.07bpp). In this table, sensitivity, specificity, and PVP are defined relative to the independent gold standard. The table does not show any obvious trends for these parameters as a function of bit rate. Sensitivity is the ratio of the number of cases a judge calls "positive" to the number of cases actually "positive" according to the independent gold standard. Here "positive" is defined as the union of categories F/U, C/B, and BX. A "negative" study is RTS. Sensitivity and specificity can be thought of as binomial issues, and so if the sensitivity is p, then the variance associated with that sensitivity is p( 1 — p). The standard deviation calculation for PVP is somewhat more complicated and is not included here; because PVP is the ratio of two random quantities (even given the gold standard), an analytical approach to the computation of variance requires approximate statistical methods related to what is called "propagation of errors'' in physics.
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