Screening mammograms by community radiologists: variability in false-positive rates

Abstract

Background: Previous studies have shown that the agreement among radiologists interpreting a test set of mammograms is relatively low. However, data available from real-world settings are sparse. We studied mammographic examination interpretations by radiologists practicing in a community setting and evaluated whether the variability in false-positive rates could be explained by patient, radiologist, and/or testing characteristics.

Methods: We used medical records on randomly selected women aged 40-69 years who had had at least one screening mammographic examination in a community setting between January 1, 1985, and June 30, 1993. Twenty-four radiologists interpreted 8734 screening mammograms from 2169 women. Hierarchical logistic regression models were used to examine the impact of patient, radiologist, and testing characteristics. All statistical tests were two-sided.

Results: Radiologists varied widely in mammographic examination interpretations, with a mass noted in 0%-7.9%, calcification in 0%-21.3%, and fibrocystic changes in 1.6%-27.8% of mammograms read. False-positive rates ranged from 2.6% to 15.9%. Younger and more recently trained radiologists had higher false-positive rates. Adjustment for patient, radiologist, and testing characteristics narrowed the range of false-positive rates to 3.5%-7.9%. If a woman went to two randomly selected radiologists, her odds, after adjustment, of having a false-positive reading would be 1.5 times greater for the radiologist at higher risk of a false-positive reading, compared with the radiologist at lowest risk (95% highest posterior density interval [similar to a confidence interval] = 1.17 to 2.08).

Conclusion: Community radiologists varied widely in their false-positive rates in screening mammograms; this variability range was reduced by half, but not eliminated, after statistical adjustment for patient, radiologist, and testing characteristics. These characteristics need to be considered when evaluating false-positive rates in community mammographic examination screening.

Fig. 1

Observed false-positive rates for 24 radiologists reading 8734 mammograms. Each column represents a single radiologist. The number of mammograms interpreted by a given radiologist is given at the base of the column and the false-positive rate is plotted on the y-axis, with the exact number describing the false-positive rate for an individual radiologist given at the top of the respective column.

Fig. 2

Results of statistical modeling for observed (unadjusted, line A) and adjusted (lines B, C, and D) false-positive rates for 24 radiologists. The details of the adjustments are given below. The right side shows the odds ratios (ORs) with 95% highest posterior density intervals (HPDs) (similar to classical 95% confidence intervals). Line A shows observed unadjusted false-positive rates and summary OR values. Line B shows false-positive rates and summary ORs after adjusting for correlation between multiple mammograms within the same woman and by the same radiologist. Line C shows ORs after adjustments given at line B, plus adjustment for patient characteristics and testing characteristics. Line D shows all adjustments at line C plus adjustment for radiologists' characteristics.