A propensity score approach to correction for bias due to population stratification using genetic and non‐genetic factors

Confounding due to population stratification (PS) arises when differences in both allele and disease frequencies exist in a population of mixed racial/ethnic subpopulations. Genomic control, structured association, principal components analysis (PCA), and multidimensional scaling (MDS) approaches have been proposed to address this bias using genetic markers. However, confounding due to PS can also be due to non‐genetic factors. Propensity scores are widely used to address confounding in observational studies but have not been adapted to deal with PS in genetic association studies. We propose a genomic propensity score (GPS) approach to correct for bias due to PS that considers both genetic and non‐genetic factors. We compare the GPS method with PCA and MDS using simulation studies. Our results show that GPS can adequately adjust and consistently correct for bias due to PS. Under no/mild, moderate, and severe PS, GPS yielded estimated with bias close to 0 (mean=?0.0044, standard error=0.0087). Under moderate or severe PS, the GPS method consistently outperforms the PCA method in terms of bias, coverage probability (CP), and type I error. Under moderate PS, the GPS method consistently outperforms the MDS method in terms of CP. PCA maintains relatively high power compared to both MDS and GPS methods under the simulated situations. GPS and MDS are comparable in terms of statistical properties such as bias, type I error, and power. The GPS method provides a novel and robust tool for obtaining less‐biased estimates of genetic associations that can consider both genetic and non‐genetic factors. Genet. Epidemiol. 33:679–690, 2009. © 2009 Wiley‐Liss, Inc.     

Comparison of QCT-derived and DXA-derived areal bone mineral density and T scores

Summary  Two-dimensional areal bone mineral density (aBMD) of the proximal femur measured by three-dimensional quantitative computed tomography (QCT) in 91 elderly women was compared to dual-energy X-ray absorptiometry (DXA) aBMD results measured in the same patients. The measurements were highly correlated, though QCT aBMD values were marginally lower in absolute units. Transformation of the QCT aBMD values to T score values using National Health and Nutrition Examination Survey (NHANES) DXA-derived reference data improved agreement and clinical utility. Introduction  World Health Organization guidelines promulgate aBMD (g cm⁻²) measurement of the proximal femur for the diagnosis of bone fragility. In recent years, there has been increasing interest in QCT to facilitate understanding of three-dimensional bone structure and strength. Objective  To assist in comparison of QCT-derived data with DXA aBMD results, a technique for deriving aBMD from QCT measurements has been developed. Methods  To test the validity of the QCT method, 91 elderly females were scanned on both DXA and CT scanners. QCT-derived DXA equivalent aBMD (QCT_DXA aBMD) was calculated using CTXA Hip™ software (Mindways Software Inc., Austin, TX, USA) and compared to DXA-derived aBMD results. Results  Test retest analysis indicated lower root mean square (RMS) errors for CTXA; F test between CTXA and DXA was significantly different at femoral neck (FN) and trochanter (TR) (p < 0.05). QCT underestimates DXA values by 0.02 ± 0.05 g cm⁻² (total hip, TH), 0.01 ± 0.04 g cm⁻² (FN), 0.03 ± 0.07 g cm⁻² (inter-trochanter, IT), and 0.02 ± 0.05 g cm⁻² (TR). The RMS errors (standard error of estimate) between QCT and DXA T scores for TH, FN, IT, and TR were 0.36, 0.40, 0.39, and 0.49, respectively. Conclusions  This study shows that results from QCT aBMD appropriately adjusted can be evaluated against NHANES reference data to diagnose osteoporosis.     

Residency applicants misinterpret their United States Medical Licensing Exam Scores

Proper interpretation of the results of the United States Medical Licensing Exam (USMLE) is important for program directors, residents, and faculty who advise applicants about applying for residency positions. We suspected that applicants often misinterpreted their performance in relationship to others who took the same examination. In 2005, 54 consecutive applicants to the University of Tennessee, College of Medicine internal medicine residency program were asked to complete a brief survey about their performance on Parts 1 and 2 of the USMLE exam. When asked what percentile their Part I score represented, slightly over one in ten were unsure or did not know, and nearly three out of five wrote in their two-digit score. Of the 15 who wrote in another number, only a third were within ten percentile points of their estimated percentile. Similar results were seen for Part II. A higher percentage of international medical graduates (IMGs) than U.S. applicants responded to the percentile question with their two-digit scores (79% vs. 50% p = .08). Applicants to residency programs frequently misinterpret their performance on the USMLE compared to their peers. Unless they are high performers, those who misinterpret their two-digit scores as percentiles markedly overestimate their performance. The sponsors of the USMLE should discontinue reporting the two-digit score and consider re-instating the reporting of percentiles.     

试题库在预防医学课程考核中的应用效果分析

目的 了解新乡医学院三全学院不同专业医学生预防医学课程考试情况,促进课程考核方式和试题库建设质量的提高.方法 运用教育测量学的原理和方法,对试卷的质量和学生的成绩进行分析.结果 本次考试学生的平均成绩为72.73分,呈正态分布.不同专业学生的考试成绩差异具有统计学意义( P＜0.001).试卷平均难度、区分度和信度分别为0.61、0.43和0.71.结论 试卷题型分布合理、难度适中、区分度尚可、信度高,试题库可以用于课程考核.同时,还需要加强不同专业学生预防医学课程的教育力度.     

高血压患者踝臂指数与冠状动脉狭窄严重程度的相关性研究

目的观察老年高血压患者踝臂指数与冠状动脉狭窄严重程度的相关性,评价踝臂指数对冠状动脉狭窄严重程度的预测价值。方法连续入选156例接受冠状动脉造影检查的老年高血压患者（年龄≥65岁）进行研究,根据冠状动脉造影结果分为无病变组（16例）、单支病变组（20例）、2支病变组（28例）、3支或左主干病变组（92例）。对所有患者进行病史采集、血液化验检查和踝臂指数测量,并对踝臂指数与冠状动脉Gensini评分做相关分析。结果踝臂指数与Gensini评分呈负相关;冠状动脉3支或左主干病变组患者踝臂指数显著降低（P〈0.01）,而造影正常、单支病变或2支病变组患者踝臂指数无显著差异;评价踝臂指数对3支或左主干病变预测价值的ROC曲线下面积为（0.79±0.036）,95%可信区间为（0.69～0.85,P〈0.001）;踝臂指数≤0.9作为截断值预测3支或左主干病变具有相对高的特异性（89.5%）和敏感性（53.6%）。结论老年高血压患者踝臂指数与冠状动脉狭窄严重程度呈负相关,踝臂指数≤0.9对预测冠状动脉3支和左主干病变具有较高的特异性和敏感性。     

The evolving clinical scenario of myelodysplastic syndrome: the need for a complete and up to date upfront diagnostic assessment

Until the beginning of the current millennium, few concrete therapeutic possibilities were available for myelodysplastic syndrome (MDS) patients. This situation has dramatically changed in the last decade when new knowledge, new drugs and new opportunities have become available for physicians and their MDS patients. A correct diagnostic and prognostic assessment of all MDS patients wherever they are first seen in a hematology or internal medicine department is mandatory to identify the best therapeutic option and the most appropriate resources allocation. This article will review modern diagnostic criteria and classification together with correlated new therapeutic opportunities.     

两种浓度缩宫素用于延期妊娠促宫颈成熟及引产与宫颈形态的变化

目的:通过对延期妊娠孕妇静脉滴注0.2%与0.5%两种浓度缩宫素,比较其促宫颈成熟及引产效果和超声下宫颈形态的变化。方法:对227例孕41～41+6周延期妊娠孕妇随机分成两组,各静脉滴注1种浓度缩宫素,比较两种浓度缩宫素促宫颈成熟及引产效果。结果:宫颈Bishop评分<7分者,两种浓度缩宫素提高宫颈评分差异无统计学意义(P>0.05),宫颈Bishop评分≥7分者,两种浓度缩宫素分娩率差异有统计学意义(P<0.05),并与超声监测下宫颈形态变化呈一致性。结论:低浓度缩宫素能产生有效宫缩,促宫颈成熟引产安全有效。宫颈Bishop评分<7分者,0.2%缩宫素发生胎儿窘迫率低,可作为促宫颈成熟引产首选;宫颈Bishop评分≥7分者,0.5%缩宫素促宫颈成熟引产催产效果好。     

Application of the pediatric risk of mortality (PRISM) score and determination of mortality risk factors in a tertiary pediatric intensive care unit

INTRODUCTION:

To establish disease severity at admission can be performed by way of the mortality prognostic. Nowadays the prognostic scores make part of quality control and research. The Pediatric Risk of Mortality (PRISM) is one of the scores used in the pediatric intensive care units.

OBJECTIVES:

The purpose of this study is the utilization of the PRISM and determination of mortality risk factors in a tertiary pediatric intensive care unit.

METHODS

: Retrospective cohort study, in a period of one year, at a general tertiary pediatric intensive care unit. The pediatric risk of mortality scores corresponding to the first 24 hours of hospitalization were recorded; additional data were collected to characterize the study population.

RESULTS:

359 patients were included; the variables that were found to be risk factors for death were multiple organ dysfunction syndrome on admission, mechanical ventilation, use of vasoactive drugs, hospital‐acquired infection, parenteral nutrition and duration of hospitalization (p < 0,0001). Fifty‐four patients (15%) died; median pediatric risk of mortality score was significantly lower in patients who survived (p = 0,0001). The ROC curve yielded a value of 0.76 (CI 95% 0,69–0,83) and the calibration was shown to be adequate.

DISCUSSION:

It is imperative for pediatric intensive care units to implement strict quality controls to identify groups at risk of death and to ensure the adequacy of treatment. Although some authors have shown that the PRISM score overestimates mortality and that it is not appropriate in specific pediatric populations, in this study pediatric risk of mortality showed satisfactory discriminatory performance in differentiating between survivors and non‐survivors.

CONCLUSIONS:

The pediatric risk of mortality score showed adequate discriminatory capacity and thus constitutes a useful tool for the assessment of prognosis for pediatric patients admitted to a tertiary pediatric intensive care units.