PubMed Health⌕ Search

Biomedical subjects

X H Zhou

Publications and source records attributed to X H Zhou.

At least 19 recordsLinked to original sources
PubMed1998

Effectiveness of computer-generated reminders for increasing discussions about advance directives and completion of advance directive forms. A randomized, controlled trial.

BACKGROUND: Physicians can increase the rate of completion of advance directive forms by discussing directives with their patients, but the means by which physicians can be induced to initiate these discussions are unclear. Computer-generated reminders have been shown to increase physician compliance with practice guidelines. OBJECTIVE: To determine the effects of computer-generated reminders to physicians on the frequency of advance directive discussions between patients and their primary caregivers and the frequency of consequent establishment of advance directives. DESIGN: Randomized, controlled trial with a 2 x 2 factorial design. SETTING: An outpatient general medicine practice associated with an urban public hospital. PARTICIPANTS: Participants were 1) 1009 patients who were at least 75 years of age or were at least 50 years of age with serious underlying disease and 2) 147 primary care physicians (108 housestaff and 39 faculty). INTERVENTION: Computer-generated reminders that recommended discussion of one or both of two types of advance directives compared with no reminders. MEASUREMENTS: Discussions about advance directives, determined by patient interviews after all scheduled patient-physician outpatient encounters, and completed advance directive forms. The study period was approximately 1 year. RESULTS: Physicians who did not receive reminders (controls) discussed advance directives with 4% of the study patients compared with 24% for physicians who received both types of reminders (adjusted odds ratio, 7.7 [95% CI, 3.4 to 18]; P < 0.001). Physicians who did not receive reminders completed advance directive forms with only 4% of their study patients compared with 15% for physicians who received both types of reminders (adjusted odds ratio, 7.0 [CI, 2.9 to 17]; P < 0.001). Overall, 45% of patients with whom advance directives were discussed completed at least one type of advance directive. CONCLUSIONS: Simple computer-generated reminders aimed at primary caregivers can increase the rates of discussion of advance directives and completion of advance directive forms among elderly outpatients with serious illnesses.

Advance Care Planning↗
PubMed1997

Methods for comparison of cost data.

BACKGROUND: Researchers are increasingly interested in examining costs of care, and large administrative and clinical databases have made relevant data readily available. Because a few patients incur high costs relative to most patients, the distribution of cost data is often skewed. How robust are the usual methods of cost analysis against the skewed distribution of cost data? OBJECTIVE: To determine the methods commonly used for comparing cost data, describe their limitations, and provide an alternate method of analysis. DESIGN: Review of statistical methods used in studies of medical costs published in medical journals between January 1991 and January 1996. Description of a Z-score method appropriate for testing the equality of mean costs between two log-normal samples; and reanalysis of published two-sample comparison results done by using the Z-score method. RESULTS: For two-sample comparisons, three methods were commonly used: the Student t-test on untransformed costs, the Wilcoxon test on untransformed costs, and the Student t-test on log-transformed costs. The t-test on untransformed costs ignores the skewness in cost data, the Wilcoxon test ignores unequal variances, and the t-test on log-transformed costs tests the wrong null hypothesis unless variances in the log-scale are equal. Eleven articles included two-sample tests and had enough information to allow reanalysis of the data using the Z-score method. These articles described a total of 23 Wilcoxon tests and 24 t-tests on untransformed costs. Most results did not change on reanalysis, but six results changed enough to alter conclusions. Specifically, reanalysis of data for which one Wilcoxon test had shown statistically significant results showed nonsignificant results; reanalysis of data for which two Wilcoxon tests had shown nonsignificant results showed statistically significant results. In articles that used t-tests on untransformed costs, two statistically significant results became nonsignificant on reanalysis and one nonsignificant result became statistically significant on reanalysis. CONCLUSIONS: The methods commonly used to compare costs of two groups have limitations. Some limitations may change some conclusions, and the direction of the change cannot be predicted. The Z-score method is designed to adjust for skewness in cost data and is appropriate for comparing means of log-normally distributed cost data.

Costs and Cost Analysis↗
PubMed1997

An empirical comparison of two semi-parametric approaches for the estimation of covariate effects from multivariate failure time data.

We conducted a simulation study to compare two semi-parametric approaches for the estimation of covariate effects from multivariate failure time data. The first approach was developed by Wei, Lin and Weissfeld (WLW) and the second by Liang, Self and Chang (LSC). Based on the simulation results we recommend Wei, Lin and Weissfeld's method for the situations with identical covariates and high correlations between the failure times. When the covariates are independent, LSC produces smaller mean squared errors than WLW, although at the expense of larger bias. We also compared four computer programs for implementing Wei, Lin and Weissfeld's approach: a FORTRAN program, MULCOX2; a SAS macro; the coxph function in S-plus, and a specialized software package for complex survey data (SUDAAN). Our comparison indicates that for large data sets, the speeds of the SAS macro and coxph are comparable, while MULCOX2- and SUDAAN took longer to run. However, MULCOX2 and coxph function in S-plus have the advantage of allowing time-dependent covariates, and SUDAAN has the advantage of handling complex survey data.

Adult↗
PubMed1997

Confidence intervals for the log-normal mean .

In this paper we conduct a stimulation study to evaluate coverage error, interval width and relative bias of four main methods for the construction of confidence intervals of log-normal means: the naive method; Cox's method; a conservative method; and a parametric bootstrap method. The simulation study finds that the naive method is inappropriate, that Cox's method has the smallest coverage error for moderate and large sample sizes, and that the bootstrap method has the smallest coverage error for small sample sizes. In addition, Cox's method produces the smallest interval width among the three appropriate methods. We also apply the four methods to a real data set to contrast the differences.

Bias↗
PubMed1997

Examination of racial differences in management of cardiovascular disease.

OBJECTIVES: We sought to identify the clinical characteristics associated with, and to investigate the impact of cohort selection criteria on, interracial use of invasive cardiac procedures and to determine survival. BACKGROUND: Although interracial differences in the use of invasive cardiac procedures have been previously reported, the underlying reasons are not known. METHODS: A retrospective cohort study was conducted at a Veterans Affairs Medical Center. Study patients were evaluated for cardiovascular disease between January 1 and December 31, 1993. RESULTS: The study included 1,406 male patients (85% white, 58% married), with a mean age of 63.4 years. African Americans were less likely than whites to undergo procedures (cardiac catheterization: odds ratio [OR] 0.37, 95% confidence interval [CI] 0.24 to 0.58; coronary angioplasty: OR 0.60, 95% CI 0.25 to 1.49; coronary bypass surgery: OR 0.22, 95% CI 0.08 to 0.63; any procedure: OR 0.32, 95% CI 0.21 to 0.50). On bivariate analysis, patients who underwent cardiac procedures were more likely to be younger, married and reside nonlocally and less likely to have severe comorbid disease; however, African Americans were less likely to be married and to reside nonlocally and more likely to have severe comorbid disease. Cohorts adjusting for referral status and specified cardiac diagnoses reduced or reversed interracial treatment differences. Thirty-day and 1-year survival rates (96% and 87.6%, respectively) were equivalent. CONCLUSIONS: Racial disparity in invasive cardiac procedure use may be partially explained by clinical differences and cohort selection bias. Despite treatment differences, survival rates were equivalent in African Americans and whites.

Black or African American↗
PubMed1997

Preferences of physicians and their patients for end-of-life care.

OBJECTIVE: Both physicians and patients view advance directives as important, yet discussions occur infrequently. We assessed differences and correlations between physicians' and their patients' desires for end-of-life care for themselves. MEASUREMENTS AND MAIN RESULTS: Study physicians (n = 78) were residents and faculty practicing in an inner-city, academic primary care general internal medicine practice. Patients (n = 831) received primary care from these physicians and were either at least 75 or between 50 and 74 years of age, with selected morbid conditions. Physicians and patients completed identical questionnaires that included an assessment of their preferences for six specific treatments if they were terminally ill. There were significant differences between physicians' and patients' preferences for all six treatments (p < .0001), with physicians wanting less treatment than their patients for five of them. Patients desiring more care (p < .01) were more often male (odds ratio [OR] 1.7). African-American (OR 1.6), and older (OR 1.02 per year). There were no such correlates with physicians' preferences. A treatment preference score was calculated from respondents' desires to receive or refuse the six treatments. Physicians' scores were highly correlated with those of their enrolled primary care patients (r = .51, p < .0001). CONCLUSIONS: Although patients and physicians as groups differ substantially in their preferences for end-of-life care, there was significant correlation between individual academic physicians' preferences and those of their primary care patients. Reasons for this correlation are unknown.

Adult↗
PubMed1997

Detection of thyroid remnant/metastasis without stunning: an ongoing dilemma.

The use of 131I doses of several mCi for scans can stun the thyrocytes and thyroid cancer cells, whereas the usual dose (300 microCi) of 123I does not. We compared the diagnostic accuracy of the 123I (300 microCi) scans and that of 131I (3-10 mCi) scans in 155 patients. The diagnostic accuracy of a 123I scan in detecting functioning thyroid remnant/metastasis was 89.5% (77/86 scans) and that of a 131I scan was 92.9% (39/42) in 6 week-postoperative patients (p = 0.750). For radioablation therapy follow-up patients, the diagnostic accuracy of 123I in determining presence or absence of functioning remnant or metastasis was 69.4% (25/36) and that of 131I was 92.5% (49/53) with a p value of 0.079. The success rates for complete ablation of functioning tissue after radioiodine therapy administered after diagnostic 123I and after 131I were 72% (34/47) and 56% (24/43), respectively, with a p value of 0.125. Our study indicates the following: 1) for the first postoperative evaluation, the diagnostic accuracy of the 123I scan was essentially equal to that of the 131I scan, and the success rate of radioablation therapy appears to be better than 123I scan; and 2) for postablation follow-up surveys, the 131I scan appears to be better but carries the risk of stunning the functioning cells.

Adolescent↗
PubMed1997

Universal standardization of bone density measurements: a method with optimal properties for calibration among several instruments.

The International Dual-Photon X-Ray Absorptiometry (DXA) Standardization Committee (IDSC) conducted a cross-calibration study among three models of DXA machines from three different manufacturers. In that study, 100 subjects were scanned on all three machines. A set of equations were derived to convert bone mineral density (BMD) on each machine to a "standardized BMD" (sBMD) such that sBMD from the same subject derived from different machines would be approximately the same. In a reanalysis of the cross-calibration data, we showed that the conversion method used in the IDSC study did not achieve several optimal properties desirable in such conversions. We derived new conversion equations to sBMD based on minimizing differences among sBMD from the three machines. More important is that the new conversions have no residual bias that was present in the IDSC conversions. The performance of the methods were compared on the cross-calibration data as well as an external data set. We conclude that the IDSC conversions are adequate for clinical use on other machines worldwide, but that researchers should standardize their own machines in a laboratory using the new method.

Absorptiometry, Photon↗
PubMed1997

Methods for comparing the means of two independent log-normal samples.

Standard methods of using the t-test and the Wilcoxon test have deficiencies for comparing the means of two skewed log-normal samples. In this paper, we propose two new methods to overcome these deficiencies: (1) a likelihood-based approach and (2) a bootstrap-based approach. Our simulation study shows that the likelihood-based approach is the best in terms of the type I error rate and power when data follow a log-normal distribution.

Biometry↗
PubMed1996

A simple method for comparing correlated ROC curves using incomplete data.

Comparative studies of the accuracy of diagnostic procedures often use a paired design to gain in efficiency. Standard methods for analysing data from paired designs require complete observations. In many studies, however, one of the test results may be missing for some patients. In this paper, we propose a simple correction to the existing complete data methods to compare areas under ROC curves derived from paired designs. The approach makes it possible to use the entire available data set in carrying out the comparison, provided that the probability of having both tests does not depend on the test results. As an illustration, we apply our method to the analysis of data from prospective comparison of MRI and ultrasound in detecting periprostatic invasion.

Data Interpretation, Statistical↗
PubMed1996

Using electronic medical records to predict mortality in primary care patients with heart disease: prognostic power and pathophysiologic implications.

OBJECTIVE: To identify high-risk patients with heart disease by using data stored in an electronic medical record system to predict six-year mortality. DESIGN: Retrospective cohort study. SETTING: Academic primary care general internal medicine practice affiliated with an urban teaching hospital with a state-of-the-art electronic medical record system. PATIENTS: Of 2,434 patients with evidence of ischemic heart disease or heart failure or both who visited an urban primary care practice in 1986, half were used to derive a proportional hazards model, and half were used to validate it. MEASUREMENTS: Mortality from any cause within six years of inception date. Model discrimination was assessed with the C statistic, and goodness-of-fit was measured with a calibration curve and Hosmer-Lemeshow statistic. MAIN RESULTS: Of these patients 82% had evidence of ischemic heart disease, 53% heart failure, and 35% both conditions. Mean survival among the 653 (27%) who died was 2.8 years; mean follow-up among survivors was 5.0 years. Those with both heart conditions had the highest mortality rate (45% at 6 years), followed by isolated heart failure (39%) and ischemic heart disease (18%). Of 300 potential predictive characteristics, 100 passed a univariate screen and were submitted to maltivariable proportional hazards regression. Twelve variables contributed independent predictive information: age, weight, more than one previous hospitalization for heart failure, and nine conditions indicated on diagnostic tests and problem lists. No drug treatment variables were independent predictors. The model C statistic was 0.76 in the derivation sample of patients and 0.74 in a randomly selected validation sample, and it was well calibrated. Patients in the lowest and highest quartiles of risk differed more than five-fold in their average risk. CONCLUSIONS: Routine clinical data stored in patients electronic medical records are capable of predicting mortality among patients with heart disease. This could allow increasingly scarce health care resources to be focused on those at highest mortality risk.

Aged↗
PubMed1996

Risk factors for delirium tremens development.

OBJECTIVE: To identify clinical characteristics associated with inpatient development of delirium tremens so that future treatment efforts can focus on patients most likely to benefit from aggressive therapy. DESIGN: Retrospective cohort study among patients discharged with diagnoses related to alcohol abuse. SETTING: University-affiliated inner-city hospital. PATIENTS/PARTICIPANTS: Two hundred consecutive patients discharged between June 1991 and August 1992 who underwent evaluation and treatment for alcohol withdrawal or detoxification. MEASUREMENTS AND MAIN RESULTS: Mean age was 41.9 years, 85% were male, 57% were white and 84% were unmarried. Forty-eight (24%) of the patients developed delirium tremens during hospitalization. Bivariate analysis indicated that those who developed delirium tremens were more likely to be African-American, unemployed, and homeless, and were more likely to have gone more days since their last drink, and to have concurrent acute medical illness, high admission blood urea nitrogen level and respiratory rate, and low admission albumin level and systolic blood pressure. In multiple logistic regression analyses, patients who developed delirium tremens were more likely to have gone more days since their last drink (odds ratio [OR] 1.3; 95% confidence interval [CI] 1.09, 1.61) and to have concurrent acute medical illness (OR 5.1; 95% CI 2.07, 12.55). These risk factors were combined for assessment of their ability to predict the occurrence of delirium tremens. If no factors were present, 9% developed delirium tremens; if one factor was present, 25% developed delirium tremens; and if two factors were present, 54% developed delirium tremens. CONCLUSIONS: Inpatient development of delirium tremens was common among patients treated for alcohol detoxification or withdrawal and correlated with several readily available clinical variables.

Adult↗
PubMed1996

Transjugular intrahepatic portosystemic shunt procedure: efficacy of 10-mm versus 12-mm Wallstents.

PURPOSE: To compare results of transjugular intrahepatic portosystemic shunt (TIPS) placement with 10- and 12-mm Wallstents. MATERIALS AND METHODS: Forty-six TIPS procedures in 47 patients were retrospectively reviewed. Wallstents that were 10 mm in diameter were used in 23 patients, and those that were 12 mm in diameter were used in 23 patients. Immediate results were compared, which included initial portosystemic gradient and Doppler measurements of blood flow velocity through the shunt at 1 day. Long-term patency and velocities were also assessed. RESULTS: TIPS were successfully created in 46 of 47 patients (98%). In one patient in the 10-mm group, the portal vein could not be accessed. When compared with TIPS in the 10-mm group, TIPS placed in the 12-mm group required dilation to larger diameters (mean, 11.1 vs 9.2 mm; P < .0001) to achieve an identical target gradient of 10 mm Hg and exhibited lower 1-day velocities (mean, 1.3 m/sec vs 1.7 m/sec; P < .03). The 1-day occlusion rate was 17% (four of 23 patients) in the 12-mm group versus 0% in the 10-mm group (P < .02). Patient survival was statistically significantly less in the 12-mm group (P < .03). CONCLUSION: Twelve-millimeter Wallstents yield statistically significantly poorer short- and long-term results in TIPS procedures. This is most likely due to the decreased radial strength of the larger stent, which is 50% less than that of the 10-mm stent.

Adolescent↗
PubMed1996

Pulmonary emboli from pulse-spray and mechanical thrombolysis: evaluation with an animal dialysis-graft model.

PURPOSE: To compare pulmonary emboli resulting from pulse-spray pharmacomechanical thrombolysis (PSPMT) and mechanical thrombolysis performed to declot dialysis-access grafts. MATERIALS AND METHODS: Polytetrafluoroethylene arteriovenous shunts were created in eight dogs and were deliberately clotted at monthly intervals. Animals were randomly assigned to treatment with pulse-spray urokinase thrombolysis or a low-speed rotational percutaneous thrombolytic device. Perfusion imaging, pulmonary-artery pressure measurements, and pulmonary arteriography were performed before and after each procedure. RESULTS: A total of 22 procedures were performed (11 PSPMT and 11 mechanical thrombolysis). Declotting was successful in all procedures, with 100% 30-day patency. Segmental defects were seen on perfusion images after 10 (91%) of 11 PSPMT procedures and two (18%) of 11 mechanical thrombolysis procedures (P < .002). Transient increases in pulmonary-artery pressure occurred in the PSPMT group. Complete resolution of emboli and return to baseline pressures were seen in all cases, even after multiple (up to four) procedures in the same animal. There was no histologic evidence of pulmonary infarction in either group. CONCLUSION: The percutaneous thrombolytic device is effective for declotting dialysis grafts in dogs and results in statistically significantly fewer pulmonary emboli compared with PSPMT.

Animals↗
PubMed1996

A nonparametric maximum likelihood estimator for the receiver operating characteristic curve area in the presence of verification bias.

The efficacy of a diagnostic test can be represented by the area under the receiver operating characteristic (ROC) curve. In estimating the ROC curve area, a common problem is verification bias resulting from selectively verifying a subset of patients initially tested. This paper proposes a simple verification bias correction procedure for estimating the ROC curve area and its corresponding variance.

Bias↗
PubMed1995

Binding characterization of the iron transport receptor from the outer membrane of Escherichia coli (FepA): differentiation between FepA and FecA.

The dissociation constants for the binding of ferric enterobactin with FepA and FecA are quantitated with displacement experiments. It is found that Kd for FepA is 12 times lower than the one for FecA. This indicates that FepA is an high-affinity receptor while FecA binds ferric enterobactin with a lower affinity. Monoclonal antibodies specific for binding epitopes of FepA inhibit the binding of ferric enterobactin with purified FepA. These same antibodies do not inhibit the binding of ferric enterobactin with purified FecA. This indicates that the binding epitopes in FecA and FepA are different.

Bacterial Outer Membrane Proteins↗
PubMed1995

Pancreatic adenocarcinoma: CT versus MR imaging in the evaluation of resectability--report of the Radiology Diagnostic Oncology Group.

PURPOSE: To compare findings with computed tomography (CT) and magnetic resonance (MR) imaging in pancreatic adenocarcinoma and to determine optimal pulse sequences for MR imaging. MATERIALS AND METHODS: CT scans and MR images were compared of 189 adult patients with known or suspected adenocarcinoma of the pancreas. Levels of confidence were correlated with surgical and pathologic results. RESULTS: The accuracy of CT was 0.73 and of MR imaging was 0.70. The negative predictive value of CT was 0.28 and of MR imaging was 0.23. The positive predictive value of CT was 0.89 and of MR imaging was 0.88. Gradient-echo and T1-weighted spin-echo sequences ranked equally in evaluation of vascular invasion, T1-weighted spin-echo sequences were preferred for assessing lymphadenopathy, and T2-weighted spin-echo sequences were preferred for detecting hepatic metastases. CONCLUSIONS: Cross-sectional imaging modalities are useful in the identification of unresectable pancreatic carcinoma. CT is recommended for initial imaging assessment.

Adenocarcinoma↗