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Penalization is a very general method of stabilizing or regularizing estimates, which has both frequentist and Bayesian rationales. We consider some questions that arise when considering alternative penalties for logistic regression and related models. The most widely programmed penalty appears to be the Firth small‐sample bias‐reduction method (albeit with small differences among implementations and the results they provide), which corresponds to using the log density of the Jeffreys invariant prior distribution as a penalty function. The latter representation raises some serious contextual objections to the Firth reduction, which also apply to alternative penalties based on t‐distributions (including Cauchy priors). Taking simplicity of implementation and interpretation as our chief criteria, we propose that the log‐F(1,1) prior provides a better default penalty than other proposals. Penalization based on more general log‐F priors is trivial to implement and facilitates mean‐squared error reduction and sensitivity analyses of penalty strength by varying the number of prior degrees of freedom. We caution however against penalization of intercepts, which are unduly sensitive to covariate coding and design idiosyncrasies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
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IntroductionA valid day of accelerometry is commonly defined as an absolute duration of wear time. Data processing inconsistencies can arise when using absolute valid-day criteria for adults with varied waking hours. The aim was to compare the use of absolute and relative valid-day criteria in a sample of adults with mental illness.MethodsData were from 99 non-institutionalised adults with mental illness. Participants were asked to wear an ActiGraph GT3X+ accelerometer continuously for seven days, and to note sleep and non-wear times. Absolute valid-day criteria were defined as a set number of hours/day, and relative criteria as a proportion of waking hours. The mean waking duration, non-wear time, and time spent in physical activity (PA) and sedentary behaviour (SB), were derived from accelerometer data, and compared for a range of absolute and relative criteria. The potential inaccuracy of PA and SB estimates were also estimated.ResultsUse of absolute criteria systematically biased the sample toward those with longer waking hours, and resulted in a median of 86% (IQR = 47%–198%) more non-wear time than relative criteria. The potential inaccuracy of SB was from −2.5% to 0% with relative criteria, and from −2.2% to 10.6% for absolute criteria.ConclusionsFor participant samples with varied waking hours, such as adults with mental illness, a valid-day criterion should be based on the proportion of waking hours, rather than the absolute time. The specific valid-day criterion should be chosen for each study independently, and be accompanied with a measure of the non-wear time.  相似文献   
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闭合复位空心钉内固定后踝骨折的疗效分析   总被引:1,自引:0,他引:1  
目的 比较闭合复位空心钉内固定和切开复位的疗效。方法 2011年1月至2013年6月在我院就诊的后踝骨折101例,分观察组和对照组,观察组为56例闭合复位和空心钉内固定,对照组为45例切开复位和空心钉内固定治疗,观察两组术后的疗效,手术时间,术中出血年,骨折愈合时间,完全负重时间,并发症的发生率和踝关节功能。结果 观察组的总有效率为92.86%,对照组的总有效率为95.56%,两组的总有效率差异无统计学意义(χ2=0.022,P>0.05)。两组的手术时间,踝关节稳定,行走能力,跑步能力和X线测量评估差异无统计学意义(P>0.05),而观察组的术后出血量,骨折愈合时间,完全负重时间和并发症,踝关节功能的疼痛,活动范围和总分明显短于或者少于对照组(P<0.05或P<0.01)。结论 闭合性复位和空心钉治疗后踝骨折具有创伤小,恢复快,并发症少,踝关节功能影响小等特点。  相似文献   
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IntroductionThalidomide causes congenital defects in children, such as limb reduction defects. Currently, it is used for a few indications; in Brazil, where leprosy is endemic, thalidomide is used for the treatment of erythema nodosum leprosum, and recent cases of thalidomide embryopathy have been reported.MethodsWe analyzed the frequency of births with phenotypes consistent with thalidomide embryopathy (TEP) and correlated this with the distribution of thalidomide and the prevalence of leprosy between 2005 and 2010 in Brazil.ResultsA total of 5,889,210 thalidomide tablets were distributed; the prevalence of limb reduction defects was 1.60 (CI95%: 1.54–1.66) and TEP was 0.11 (CI95%: 0.10–0.13) per 10,000 births. Poisson regression showed an increase in cases of TEP and limb reduction defects per 100,000 tablets dispensed. Clusters and geographical isolates were identified in several regions.ConclusionsThere is a correlation between thalidomide and TEP showing that thalidomide embryopathy should be monitored in countries where this medication is available.  相似文献   
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Quantitative susceptibility mapping (QSM) is a novel MRI technique for the measurement of tissue magnetic susceptibility in three dimensions. Although numerous algorithms have been developed to solve this ill‐posed inverse problem, the estimation of susceptibility maps with a wide range of values is still problematic. In cases such as large veins, contrast agent uptake and intracranial hemorrhages, extreme susceptibility values in focal areas cause severe streaking artifacts. To enable the reduction of these artifacts, whilst preserving subtle susceptibility contrast, a two‐level QSM reconstruction algorithm (streaking artifact reduction for QSM, STAR‐QSM) was developed in this study by tuning a regularization parameter to automatically reconstruct both large and small susceptibility values. Compared with current state‐of‐the‐art QSM methods, such as the improved sparse linear equation and least‐squares (iLSQR) algorithm, STAR‐QSM significantly reduced the streaking artifacts, whilst preserving the sharp boundaries for blood vessels of mouse brains in vivo and fine anatomical details of high‐resolution mouse brains ex vivo. Brain image data from patients with cerebral hematoma and multiple sclerosis further illustrated the superiority of this method in reducing streaking artifacts caused by large susceptibility sources, whilst maintaining sharp anatomical details. STAR‐QSM is implemented in STI Suite, a comprehensive shareware for susceptibility imaging and quantification. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
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