Mammography facilities vary in their size, organization, services, and processes, but it is not known whether any of these facility differences affect the interpretive performance of diagnostic mammography. In this multisite cross-sectional study, we found that US facilities have statistically significant variability in the false-positive rates of diagnostic mammography after adjusting for patient and radiologist factors. Reporting that concerns about malpractice increased additional diagnostic testing at the facility was associated with a statistically significantly higher false-positive rate and a non–statistically significantly higher sensitivity. A non–statistically significant association was also noted between a greater false-positive rate and offering specialized interventional services. Off-site interpretation of diagnostic mammograms, which occurred in three facilities in this study, was non–statistically significantly associated with lower sensitivity than facilities with on-site reading. None of the facility characteristics we assessed were associated with changes in overall accuracy.
The extensive variability in interpretive performance that we noted was markedly reduced after adjustment for patient and radiologist characteristics. Statistically significant variability was present for sensitivity and PPV2 in unadjusted analyses, but after accounting for differences in patient and radiologist characteristics, the variation was reduced. Our sample was based on 20
019 diagnostic mammograms, but some low-volume facilities had few cancers detected, as demonstrated by the wide confidence intervals around the individual facility sensitivity values and PPV2 values demonstrated in . Because sensitivity and PPV2 depend on the number of breast cancers detected, which is a relatively infrequent outcome, low statistical power may have affected our analyses.
Detailed patient and radiologist data allowed us to discriminate facility-level associations from those due to patient and radiologist factors. We sequentially assessed interpretive performance adjusted for patient factors; then for patient and radiologist factors; and finally for patient, radiologist, and multiple facility-level characteristics. The facility traits associated with performance changed dramatically after adjustment for patient attributes, then were consistent with additional adjustment for radiologist factors, and diminished when multiple facility factors were also included. These analyses suggest that the factors most strongly associated with interpretive performance for diagnostic mammograms are characteristics of a patient, such as age, breast density, time since last mammogram, and self-reported breast lump. These patient factors may differ substantially across facilities. Many health and insurance agencies encourage or publish “report cards” and quality rating systems for physicians and hospitals (21
). We caution that analyses comparing differences among mammography facilities that do not adjust for important characteristics of patients using the facility may falsely conclude that there is more facility variation than actually exists or that one facility is above or below average.
Reported concerns about malpractice were the predominant factors associated with interpretive performance at the facility level, above all the other facility characteristics measured. The influence of malpractice on US radiologists is postulated to play a role in higher recall rates in the United States than in other countries (22
). In a previous report of 124 US radiologists, 118 of whom were also participants in this study (13
), the majority (58.5% or 72 of 123) indicated that malpractice concerns moderately or greatly increased their recommendations for biopsy examinations after screening mammograms. However, the data did not demonstrate that they had higher recall and false-positive rates for screening mammograms than their colleagues without such perceptions (13
). In this facility study, belief that malpractice concerns at the facility level moderately to greatly increased recommendations for diagnostic evaluations was associated with a higher false-positive rate and non–statistically significantly higher sensitivity. It is possible that when the clinical level of perceived patient risk of breast cancer is higher, as in diagnostic mammograms compared with screening examinations, the effect of malpractice concern is more pronounced and thus measurable.
We hypothesized a priori that malpractice concerns would be associated with lower overall accuracy by increasing the false-positive rate; however, we did not find any change in overall accuracy, using ROC curve analysis. Malpractice concern was associated with both an increase in false-positive rate and an increase in cancer detection. This finding suggests a shift in the threshold for calling examinations abnormal, not a true increase in the ability to discriminate between cancer-free and cancer-associated mammograms. Although false-positive examinations are associated with expense and anxiety, any attempt to lower the false-positive rate must not be at the expense of decreasing the cancer detection rate.
Facilities that offered interventional services had a non–statistically significantly higher false-positive rate (OR = 1.97, 95% CI = 0.94 to 4.1). It is plausible that if diagnostic modalities are readily available on-site, radiologists might have a lower threshold for recommending these procedures, resulting in more false-positive and true-positive examinations. It may also be that radiologists in diagnostic facilities perceive a higher probability of cancer in general and are therefore more likely than other radiologists to make a positive interpretation. Financial incentive to perform well-reimbursed interventional services may also play a role. Sensitivity was also increased in facilities offering interventional services (OR = 1.75, 95% CI = 0.47 to 6.45), although not statistically significantly, suggesting a shift in threshold for calling examinations abnormal at facilities where more interventional services are readily available.
Malpractice concerns and the availability of interventional services were associated with high false-positive rates and sensitivities, without changing overall accuracy. There is much speculation that malpractice and the ready access to technology in the United States drive the rapidly increasing costs of medical care in this country, potentially even resulting in poorer medical outcomes (24
). Our study quantitatively demonstrates associations of diagnostic performance with malpractice concerns and access to interventional services.
Three of the 32 facilities sent their diagnostic mammograms to other locations for interpretation. These facilities had a much lower sensitivity than facilities where examinations were interpreted on-site. It is possible that these three facilities were in remote locations and/or had limited staffing and thus required off-site interpretation. When facilities send examinations out for interpretation, the interpreting radiologist may have less potential for direct patient contact and could have less feedback about the outcome of positive examinations. Although these results are based on very small numbers, the accuracy of off-site interpretation of diagnostic mammograms merits further study.
A strength of this multisite study of diagnostic mammography facilities is that it represents diverse geographic regions of the United States. Another is the ability to adjust for important patient and radiologist characteristics and link to mammography performance data using BCSC information. Both facility and radiologist surveys had high response rates and assessed a broad range of characteristics.
The study also has several limitations. Concern about malpractice is a characteristic that is closely connected to the radiologist as the party with the most personal risk; however, in our study, it was assessed as a facility trait. Because most of the respondents to this survey were technologists who might have less personal fear of malpractice lawsuits than radiologists, the finding that malpractice concerns are associated with performance suggests that perhaps within facilities, there is a culture that influences radiologist's decision making. More work, specifically assessing diagnostic interpretation and radiologist-level malpractice concerns, may help clarify these findings. Another limitation involves defining diagnostic mammography. We limited our diagnostic mammograms to examinations that were designated by the radiologist as performed for evaluation of a breast problem. However, radiologist reporting of this designation includes two groups: women with a palpable lump and women with no or unknown lump status. The latter group includes a wide variety of indications—from women with breast pain and nipple discharge to women with a palpable lump that was not self-reported. It is possible that designation of diagnostic mammograms could vary between facilities (1
). Last, our results may not be generalizable to other regions of the United States or to other countries where mammography programs may have different screening guidelines and different systems and requirements for interpreting diagnostic mammograms.
In summary, false-positive rates vary statistically significantly between facilities performing diagnostic mammography and are higher at facilities where the concern about malpractice is believed to increase recommendations for diagnostic evaluations at the facility. Analyses comparing differences among mammography facilities that do not adjust for important patient characteristics may falsely conclude that there is more facility variation in overall accuracy than what actually exists.