Biomedical subjects

W B Bilker

Publications and source records attributed to W B Bilker.

42 records · Page 3Linked to original sources

PubMed1996

A semiparametric extension of the Mann-Whitney test for randomly truncated data.

In many applications, statistical data are frequently observed subject to a retrospective sampling criterion resulting in pure right-truncated data. In classical testing problems, the Mann-Whitney test is used for testing the equality of two distributions. A semiparametric extension of this test is developed for the case when truncation is present. We consider a model in which the truncation distribution is parameterized, while the lifetime distribution is left as a nonparametric component. The method is seen to be applicable to many patterns of truncation including left truncation, right truncation, and doubly truncated data for which no other nonparametric or semiparametric test is currently available. Applications of the semiparametric method are given. Simulation results indicate that for pure right-truncated data the semiparametric test is more powerful than a recent nonparametric test.

Acquired Immunodeficiency Syndrome↗

PubMed1994

Predictability of rehospitalization for schizophrenia.

This analysis examines the predictability of the course of schizophrenia using long-term follow-up data on hospital episodes in a cohort of patients from a psychiatric case register in Denmark. We focus on whether clinical and sociodemographic data collected during the first episode are related to the number of hospitalizations during follow-up and the association of patients' course of hospitalizations with the risk of being rehospitalized. A Poisson regression model and a proportional hazards model were used to address these questions. Age of onset and time to the first rehospitalization were strong early predictors of chronicity of course, as measured by the number of psychiatric hospitalizations for each schizophrenic patient. The results also show that the risk of rehospitalization depends on the previous tenures in the community.

Adolescent↗

PubMed1993

Clinical trial of cefamandole, cefazolin, and cefuroxime for antibiotic prophylaxis in cardiac operations.

A relatively large number of comparative trials of antibiotic prophylaxis in cardiac surgery have been published, many of which have serious design flaws. Despite the large number of studies, no single antibiotic regimen has emerged as clearly superior in preventing postoperative site infections. To determine if a superior regimen could be identified with a study designed to avoid flaws found in previous studies, we undertook a randomized, double-blind clinical trial of three cephalosporins. From March 1987 to February 1990, 2759 adults underwent median sternotomies: 1641 completed study participation, 203 were enrolled but were dropped from the study for protocol violations, and 815 were excluded. The characteristics of all 2759 patients were recorded with respect to case mix and infection risk factors, and the patients were followed-up by the same nurse throughout hospitalization and for 6 weeks after discharge for the assessment of infection outcome status. Of the 1641 participants, 141 (8.6%) had one or more operative site infections: 46 of 549 (8.4%) cefamandole recipients, 46 of 547 (8.4%) cefazolin recipients, and 49 of 545 (9.0%) cefuroxime recipients (p = 0.92). The sites of infection and the depth of tissue involvement were not significantly different across groups. Because no differences in effectiveness in preventing postoperative site infections were demonstrated in a rigorously designed trial, the costs of the drugs, including the costs of their preparation and delivery, may be the only variables by which to choose among these three antibiotic prophylaxis regimens.

Adult↗

PubMedDate not supplied

Posttraumatic olfactory dysfunction: MR and clinical evaluation.

PURPOSE: To evaluate the sites of injury in patients with posttraumatic olfactory deficits and to compare damage with findings on clinical olfactory tests. METHODS: Twenty-five patients with posttraumatic olfactory dysfunction were examined by means of olfactory testing, endoscopy, and MR imaging. MR surface-coil scans through the olfactory bulbs and tracts and head-coil scans of the temporal lobes were evaluated. Quantitative and qualitative gradings of damage to the olfactory bulbs, tracts, subfrontal region, hippocampus, and temporal lobes were compared with results on tests of odor identification, detection, memory, and discrimination. RESULTS: Twelve patients were anosmic, eight had severe impairment, and five were mildly impaired. Injuries to the olfactory bulbs and tracts (88% of patients), subfrontal region (60%), and temporal lobes (32%) were found, but these did not correlate well with individual olfactory test scores. Volumetric analysis showed that patients without smell function had greater volume loss in olfactory bulbs and tracts than did those posttraumatic patients who retained some sense of smell. Qualitative and quantitative assessments of damage showed few significant correlations with olfactory tests, probably because of multifocal injuries, primary olfactory nerve damage, and the constraints of a small sample size on the detection of clinically significant differences. CONCLUSION: MR imaging shows abnormalities in patients with posttraumatic olfactory dysfunction at a very high rate (88%), predominantly in the olfactory bulbs and tracts and the inferior frontal lobes.

Adolescent↗

PubMedDate not supplied

Use of preoperative MR to predict dural, perineural, and venous sinus invasion of skull base tumors.

PURPOSE: To assess the accuracy of MR imaging in predicting dural, venous sinus, and perineural invasion by skull base tumors. METHODS: The preoperative MR images of 22 patients who had resection of skull base neoplasms were evaluated for the following characteristics: dural enhancement, pial enhancement, local perineural invasion by adjacent tumor, and venous sinus invasion by tumor. The greatest width of dural enhancement was measured, and the character of dural enhancement was noted. The pathologic and surgical reports were reviewed retrospectively with specific attention to dural, venous, and local perineural invasion. RESULTS: Of the 22 patients studied, dural invasion by tumor was confirmed in eight patients, vascular invasion in six patients, and perineural invasion in four patients. The sensitivity of dural enhancement in predicting invasion was 88%, the specificity 50%, and the accuracy 64%. When enhancement and focal nodularity were present, the sensitivity remained at 88%; however, specificity was 100% and accuracy 95%. If the dural enhancement was more than 5 mm thick, sensitivity, specificity, and accuracy were 75%, 100%, and 91%, respectively. Predicting tumor invasion of the dura by the presence of pial enhancement was 50% sensitive and 100% specific. Venous sinus/jugular vein invasion was predicted with 100% sensitivity, 94% specificity, and 95% accuracy. Local perineural invasion was predicted with 100% sensitivity, 50% specificity, and 59% accuracy. CONCLUSIONS: The presence of pial enhancement, focal dural nodules, or dural thickening of more than 5 mm is highly accurate in predicting the presence of neoplastic dural invasion. Linear enhancement of dura does not imply dural infiltration by tumor. Venous invasion by tumor can be predicted accurately with preoperative MR imaging.

Adult↗

PubMedDate not supplied

Gastrointestinal tract bleeding associated with naproxen sodium vs ibuprofen.

BACKGROUND: The risk of gastrointestinal tract bleeding requiring hospitalization associated with naproxen sodium was compared with that with ibuprofen, using a prescription database to approximate over-the-counter dosing. OBJECTIVE: To evaluate the safety of naproxen sodium. METHODS: A claims database containing Ohio Medicaid data from January 1986 through February 1993 and Michigan Medicaid data from April 1983 through July 1993 was used to compare 101,318 patients dispensed naproxen sodium with 277,601 patients dispensed ibuprofen. Using a case-cohort design, all 59 patients from the full cohort who had been hospitalized with upper gastrointestinal tract bleeding (UGIB) that developed within 14 days after the first prescription for the study drugs were compared with a subcohort made up of a 10% random sample of subjects selected from the combined drug cohorts. RESULTS: The incidence of UGIB occurring within 14 days after the first prescription in the naproxen sodium cohort was 26 (0.026%) of 101,318 (95% confidence interval [CI], 0.017%-0.038%), compared with 33 (0.012%) of 277,601 patients (95% CI, 0.008%-0.017%) in the ibuprofen cohort. Overall, the use of naproxen sodium vs ibuprofen was associated with an adjusted relative risk of 2.0 (95% CI, 1.1-3.8). Among people with multiple prescriptions, the crude relative risk for those receiving therapy in a dose typical of over-the-counter use was 4.1 (95% CI, 1.2-13.8). CONCLUSIONS: The overall incidence of UGIB is low with both drugs. There is little additional absolute risk posed by the use of low-dose naproxen sodium, compared with low-dose ibuprofen, despite an increased relative risk. However, given the widespread use of these drugs, a substantial number of additional cases of UGIB could result from use of naproxen sodium. This increased risk should be considered, especially for patients whose baseline risk of UGIB is elevated.

Adolescent↗