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Figure 2: Probabilities as a function of the number of readers in a trial for observing no additional cancers detected (left), one-half or more additional cancers detected per 1000 screening mammograms (middle), and a statistically significant increase in cancer detection rate (ie, statistical power) (right), given a postulated increase of one additional cancer detected per 1000 screening mammograms. Correlation of individual readers' cancer detection rates between the two arms of a trial is not included. Variability in the observed single-reader cancer detection rates caused the discrepancies between the postulated and observed changes in cancer detection rates. Curves are grouped by single-reader total screening mammogram volume; parenthetical numbers indicate the number of readers for each volume category. See text and Figure 3 for confidence intervals. Sample sizes refer to one arm of a two-arm trial.
