Biomedical subjects

C E Phelps

Publications and source records attributed to C E Phelps.

41 records · Page 3Linked to original sources

PubMedDate not supplied

Estimating diagnostic test accuracy using a "fuzzy gold standard".

This study uses Monte Carlo methods to analyze the consequences of having a criterion standard ("gold standard") that contains some error when analyzing the accuracy of a diagnostic test using ROC curves. Two phenomena emerge: 1) When diagnostic test errors are statistically independent from inaccurate ("fuzzy") gold standard (FGS) errors, estimated test accuracy declines. 2) When the test and the FGS have statistically dependent errors, test accuracy can become overstated. Two methods are proposed to eliminate the first of these errors, exploring the risk of exacerbating the second. Both require a probabilistic (rather than binary) gold-standard statement (e.g., probability that each case is abnormal). The more promising of these, the "two-truth" method, selectively eliminates those cases where the gold standard is most ambiguous (probability near 0.5). When diagnostic test and FGS errors are independent, this approach can eliminate much of the downward bias caused by FGS error, without meaningful risk of overstating test accuracy. When the test and FGS have dependent errors, the resultant upward bias can cause test accuracy to be overstated, in the most extreme cases, even before the offsetting "two-truth" approach is employed.

Clinical Laboratory Techniques↗

PubMedDate not supplied

Good technologies gone bad: how and why the cost-effectiveness of a medical intervention changes for different populations.

Cost-effectiveness (CE) ratios vary considerably, not only across interventions, but within single interventions. Using a simple decision-tree model of the treat-vs no-treat decision to organize the analysis, four potential errors leading to these within-treatment differences in CE ratios are identified. These errors arise from estimates relating to 1) prior probabilities of disease; 2) treatment efficacies; 3) costs of treatment; and 4) patient preferences. Systematic biases, where present, suggest overuse of medical interventions. For diagnostic tests, two additional potential sources of error are considered (using a simple decision tree incorporating both test and treat decisions). These involve 5) sensitivity and specificity of the diagnostic test and 6) inappropriate choice of "cutoff" to determine abnormal patients, in part arising from errors in estimating prior probability of disease.

Cost-Benefit Analysis↗

PubMedDate not supplied

Cryotherapy in infants with retinopathy of prematurity. A decision model for treating one or both eyes.

Formal decision model analysis for cryotherapy to reduce blindness from retinopathy of prematurity shows that the decision to treat depends substantially on disease severity, the probability of long-term side effects, and correlations of treatment outcomes and side effects for individuals in whom both eyes are treated. The model indicates that both eyes should be treated regardless of disease severity only when the probability of long-term side effects is zero. As risk of long-term side effects increase, treating neither eye or only the worst eye is preferred for an increasingly large spectrum of disease. With high correlations of long-term side effects, treating the worst eye is preferred for moderate levels of disease severity. For high disease severity, treating both eyes is recommended, even when the probability of long-term side effects is high. Better-informed treatment recommendations must await new data to assess risks of long-term side effects and correlations of treatment outcomes and side effects.

Cryosurgery↗

PubMedDate not supplied

Cystic fibrosis carrier screening: knowledge and attitudes of prenatal care providers.

We are conducting a trial of population carrier screening for cystic fibrosis (CF), targeting pregnant and nonpregnant patients of prenatal care providers. We first enlisted providers by presenting a description of the trial to the obstetrical staffs of the five Rochester, New York, hospitals having delivery services. Of the 124 prenatal care providers (111 obstetricians and 13 family practitioners) with delivery privileges at the five hospitals, only 81 (65%) attended one of our presentations. Providers who attended lacked knowledge about CF screening and counseling and expressed divergent attitudes about prenatal diagnosis for carrier women having test-negative partners. Of the 79 providers completing an attitude questionnaire, 68 (86%) were willing to offer carrier screening to all their patients if educational materials, testing, and counseling were all provided without charge. After visiting participating physicians' offices to orient their staff, we reached two additional conclusions. First, in considering whether to offer CF carrier screening to their patients, prenatal care providers are less concerned about imperfect test sensitivity, false reassurance of those testing negative, or discrimination against those testing positive than about time required to answer patients' questions if they screen and about legal liability if they do not. Second, some providers are more resistant to offering screening to nonpregnant patients than to pregnant patients, not because they believe that the timing is less appropriate, but because nonpregnant patients do not routinely receive an advance mailing, have phlebotomy, or return for follow-up. Our experience raises concerns about the willingness and capability of prenatal care providers to translate advances in molecular medicine into prenatal screening services.

Attitude of Health Personnel↗

PubMedDate not supplied

The accuracy of magnetic resonance imaging in patients with suspected multiple sclerosis. The Rochester-Toronto Magnetic Resonance Imaging Study Group.

OBJECTIVE: To design and implement a methodologically rigorous study to examine the accuracy of magnetic resonance imaging (MRI) in a patient population clinically suspected of having multiple sclerosis (MS). DESIGN AND SETTING: Three hundred three patients, who were referred to two university medical centers because of the suspicion of MS, underwent MRI of the head and double-dose, contrast-enhanced computed tomography (CT) of the head. The images were read by two observers individually and without knowledge of the clinical course or final diagnosis. Patients were followed up for at least 6 months and reevaluated clinically with subsequent neurological examination. Final diagnosis (MS or not MS) was made by a panel of neurologists on the basis of the clinical findings at presentation, those that developed during follow-up, and other diagnostic tests. The results of the imaging procedures were excluded to avoid incorporation bias. Diagnostic accuracy was assessed using receiver-operating characteristic analysis and likelihood ratios. RESULTS: Magnetic resonance imaging of the head was considerably more accurate than CT in diagnosing MS. The area under the receiver-operating characteristic curve for MS was 0.82 (compared with 0.52 for CT) indicating that MRI was a good but not definitively accurate test for MS. A "definite MS" reading on an MRI of the head was specific for MS (likelihood ratio, 24.9) and essentially established the diagnosis, especially in patients clinically designated as "probable MS" before testing. However, MRI of the head was negative for MS in 25% and equivocal in 40% of the patients considered to have MS by the diagnostic review committee (sensitivity, 58%). CONCLUSIONS: Magnetic resonance imaging of the head provided assistance in the diagnosis of MS when lesions were visualized. Its ability far exceeded imaging with double-contrast CT. The sensitivity and, therefore, the predictive value of a negative MRI result for MS were, however, not sufficiently high for a normal MRI to be used to conclusively exclude the diagnosis of MS.

Adolescent↗