• 【牙周炎病例对照研究中的不参与和偏倚调整。】 复制标题 收藏 收藏
    DOI:10.1111/j.1600-0722.2008.00567.x 复制DOI
    作者列表:López R,Frydenberg M,Baelum V
    BACKGROUND & AIMS: :Periodontal researchers frequently use case-control studies, but information on participation rates and the reasons for participation are often missing in the publications, thus hindering the assessment of the validity of those studies. A nested case-control study based on a well-defined population was used to (i) describe the patterns of participation; (ii) show how some associations can be biased; and (iii) illustrate how inverse probability weights can be applied to reduce bias. Differential subject participation was quantified using the ratio between participation for each level and the overall participation. Possible biased associations were illustrated using the odds ratios found for eligible and participant subjects. Finally, we used the estimated probability that an individual participates in the case-control study conditional on that individual's covariate pattern, as observed in the screening study to attempt bias reduction. Considerable differential participation was observed for selected factors, including age, annual tuitions and fees, parental income, and parental education. The strategy used for adjustment of bias resulted in some degree of bias reduction. These findings challenge the inferential validity of many studies on periodontitis. The design and conduct of these studies should aim to improve subject participation and must consider and minimize this potential source of bias.
    背景与目标: : 牙周研究人员经常使用病例对照研究,但是出版物中经常缺少有关参与率和参与原因的信息,因此阻碍了对这些研究有效性的评估。基于明确定义的人群的嵌套病例对照研究用于 (i) 描述参与模式; (ii) 显示某些关联如何产生偏差; (iii) 说明如何应用反向概率权重来减少偏差。使用每个级别的参与与总体参与之间的比率来量化受试者的不同参与。使用合格受试者和参与者受试者的比值比说明了可能的偏倚关联。最后,我们使用了在筛选研究中观察到的以个体的协变量模式为条件的个体参与病例对照研究的估计概率,以尝试减少偏倚。对于选定的因素,包括年龄,年度学费和费用,父母收入和父母教育,观察到相当大的参与程度。用于调整偏差的策略导致一定程度的偏差减少。这些发现挑战了许多牙周炎研究的推论有效性。这些研究的设计和实施应旨在提高受试者的参与度,并且必须考虑并最大程度地减少这种潜在的偏见来源。
  • 【澳大利亚在线活跃调查的有效性和偏见: 与自我报告偏见相关的活动水平和参与者因素。】 复制标题 收藏 收藏
    DOI:10.1186/s12874-020-0896-4 复制DOI
    作者列表:Curtis RG,Olds T,Plotnikoff R,Vandelanotte C,Edney S,Ryan J,Maher C
    BACKGROUND & AIMS: BACKGROUND:This study examined the criterion validity of the online Active Australia Survey, using accelerometry as the criterion, and whether self-report bias was related to level of activity, age, sex, education, body mass index and health-related quality of life. METHODS:The online Active Australia Survey was validated against the GENEActiv accelerometer as a direct measure of activity. Participants (n = 344) wore an accelerometer for 7 days, completed the Active Australia Survey, and reported their health and demographic characteristics. A Spearman's rank coefficient examined the association between minutes of moderate-to-vigorous physical activity recorded on the Active Australia Survey and GENEActiv accelerometer. A Bland-Altman plot illustrated self-report bias (the difference between methods). Linear mixed effects modelling was used to examine whether participant factors predicted self-report bias. RESULTS:The association between moderate-to-vigorous physical activity reported on the online Active Australia Survey and accelerometer was significant (rs = .27, p < .001). Participants reported 4 fewer minutes per day on the Active Australia Survey than was recorded by accelerometry (95% limits of agreement -104 - 96 min) but the difference was not significant (t(343) = -1.40, p = .16). Self-report bias was negatively associated with minutes of accelerometer-recorded moderate-to-vigorous physical activity and positively associated with mental health-related quality of life. CONCLUSIONS:The online Active Australia Survey showed limited criterion validity against accelerometry. Self-report bias was related to activity level and mental health-related quality of life. Caution is recommended when interpreting studies using the online Active Australia Survey.
    背景与目标:
  • 【当事件条件暴露时,自我控制的病例系列中暴露前时间偏差的影响: 髋部/股骨骨折和使用苯二氮卓类药物作为案例研究。】 复制标题 收藏 收藏
    DOI:10.1002/pds.4959 复制DOI
    作者列表:Requena G,Douglas IJ,Huerta C,de Abajo F
    BACKGROUND & AIMS: BACKGROUND:In self-controlled case series (SCCS), the event should not condition the probability of subsequent exposure. If this assumption is not met, an important bias could take place. The association of hip/femur fracture (HFF) and use of benzodiazepines (BDZ) has a bidirectional causal relationship and can serve as case study to investigate the impact of this methodological issue. OBJECTIVES:To assess the magnitude of bias introduced in a SCCS when HFF conditions the posterior exposure to BDZ and explore ways to correct it. METHODS:Four thousand four hundred fifty cases of HFF who had at least one BZD prescription were selected from the primary care health record database BIFAP. Exposure to BZD was divided into non-use, current, recent, and past use. Conditional Poisson regression was used to estimate incidence rate ratios (IRRs) of HFF among current vs non-use/past, adjusted for age. To investigate possible event-exposure dependence, a pre-exposure time of different lengths (15, 30, and 60 days) was excluded from the reference category to evaluate the IRR. RESULTS:IRR of HHF for current use was 0.79 (0.72-0.86); removing 30 days, IRR was 1.43 (1.31-1.57). Removing 15 days, IRR was 1.29 (1.18-1.41), and removing 60 days, IRR was 1.56 (1.42-1.72). A pre-exposure period up to 182 days was necessary to remove such effect giving an IRR of 1.64 (1.48-1.81). CONCLUSIONS:HFF remarkably conditioned the use of BDZs resulting in seriously biased IRRs when this association was studied through a SCCS design. The use of pre-exposure periods of different lengths helped to correct this error.
    背景与目标:
  • 【优化退火温度以减少多模板PCR中引物错配引起的偏差。】 复制标题 收藏 收藏
    DOI:10.1128/AEM.67.8.3753-3755.2001 复制DOI
    作者列表:Ishii K,Fukui M
    BACKGROUND & AIMS: :To reduce PCR bias derived from a primer mismatch, the effect of the annealing temperature on the product ratio was investigated by denaturing gradient gel electrophoresis analysis of PCR products from a mixture of perfect-match and one-mismatch templates. These templates were generated by PCR from Pediococcus acidilactici for one mismatch and Micrococcus luteus for the perfect match. PCRs showed that the bias was reduced at lower temperatures. An environmental sample was also examined.
    背景与目标: : 为了减少源自引物错配的PCR偏差,通过对来自完全匹配和一错配模板的混合物的PCR产物进行变性梯度凝胶电泳分析,研究了退火温度对产物比例的影响。这些模板是通过PCR从酸性小球菌中产生的,以进行一次错配,而黄体微球菌则是完美匹配。PCRs显示,在较低的温度下,偏压降低了。还检查了环境样品。
  • 【绝经后激素的使用,筛查和乳腺癌: 偏见的特征和控制。】 复制标题 收藏 收藏
    DOI:10.1097/00001648-200107000-00013 复制DOI
    作者列表:Joffe MM,Byrne C,Colditz GA
    BACKGROUND & AIMS: :Previous investigators have suggested that screening-related biases may explain associations between postmenopausal hormone use and breast cancer. To investigate these biases, we studied postmenopausal women in the Nurses' Health Study from 1988 to 1994. Hormone use is associated with increased subsequent screening. Among women not screened in the previous 2 years, the probability difference, comparing current hormone users with others, for having mammography in the following 2 years is 19.5%; among women previously screened, the difference is 4.9%. These differences persist after control for other factors. If the increase in screening is causal, screening by mammogram could be intermediate in the causal pathway to breast cancer diagnosis. To deal with this problem, we restrict attention to a subset of the cohort in which the effect of postmenopausal hormone use on screening is small (women previously screened). In this subset, the rate ratio comparing breast cancer rates among current postmenopausal hormone users with others is 1.28. In a sensitivity analysis, the bias could not by itself plausibly account for the associations in our data. Our data provide evidence of an association between postmenopausal hormone use and breast cancer that is not solely the product of a detection bias.
    背景与目标: : 先前的研究人员认为,与筛查相关的偏见可能解释了绝经后激素使用与乳腺癌之间的关联。为了调查这些偏见,我们在护士健康研究1988年1994年中研究了绝经后妇女。激素的使用与后续筛查的增加有关。在过去2年中未进行筛查的女性中,将当前的激素使用者与其他人进行比较,在接下来的2年中进行乳房x线检查的概率差异为19.5%; 在先前筛查的女性中,差异为4.9%。在控制了其他因素之后,这些差异仍然存在。如果筛查的增加是有原因的,则通过乳房x线照片进行筛查可能是乳腺癌诊断的因果途径的中间环节。为了解决这个问题,我们将注意力集中在绝经后激素使用对筛查的影响很小的队列中的一个子集 (以前筛查过的女性)。在这个子集中,比较当前绝经后激素使用者与其他人的乳腺癌发病率的比率是1.28的。在敏感性分析中,偏差本身无法合理地解释我们数据中的关联。我们的数据提供了绝经后激素使用与乳腺癌之间关联的证据,而这不仅是检测偏倚的产物。
  • 【在慢性阻塞性肺疾病和急性冠状动脉综合征患者中比较 β 受体阻滞剂和钙通道阻滞剂的潜在偏倚证据: 一项跨国研究的结果。】 复制标题 收藏 收藏
    DOI:10.1136/bmjopen-2016-012997 复制DOI
    作者列表:Dong YH,Alcusky M,Maio V,Liu J,Liu M,Wu LC,Chang CH,Lai MS,Gagne JJ
    BACKGROUND & AIMS: OBJECTIVES:A number of observational studies have reported that, in patients with chronic obstructive pulmonary disease (COPD), β blockers (BBs) decrease risk of mortality and COPD exacerbations. To address important methodological concerns of these studies, we compared the effectiveness and safety of cardioselective BBs versus non-dihydropyridine calcium channel blockers (non-DHP CCBs) in patients with COPD and acute coronary syndromes (ACS) using a propensity score (PS)-matched, active comparator, new user design. We also assessed for potential unmeasured confounding by examining a short-term COPD hospitalisation outcome. SETTING AND PARTICIPANTS:We identified 22 985 patients with COPD and ACS starting cardioselective BBs or non-DHP CCBs across 5 claims databases from the USA, Italy and Taiwan. PRIMARY AND SECONDARY OUTCOME MEASURES:Stratified Cox regression models were used to estimate HRs for mortality, cardiovascular (CV) hospitalisations and COPD hospitalisations in each database after variable-ratio PS matching. Results were combined with random-effects meta-analyses. RESULTS:Cardioselective BBs were not associated with reduced risk of mortality (HR, 0.90; 95% CI 0.78 to 1.02) or CV hospitalisations (HR, 1.06; 95% CI 0.91 to 1.23), although statistical heterogeneity was observed across databases. In contrast, a consistent, inverse association for COPD hospitalisations was identified across databases (HR, 0.54; 95% CI 0.47 to 0.61), which persisted even within the first 30 days of follow-up (HR, 0.55; 95% CI 0.37 to 0.82). Results were similar across a variety of sensitivity analyses, including PS trimming, high dimensional-PS matching and restricting to high-risk patients. CONCLUSIONS:This multinational study found a large inverse association between cardioselective BBs and short-term COPD hospitalisations. The persistence of this bias despite state-of-the-art pharmacoepidemiologic methods calls into question the ability of claims data to address confounding in studies of BBs in patients with COPD.
    背景与目标:
  • 【基于社区的心肌梗塞研究中的参与偏倚评估,2002-2005。】 复制标题 收藏 收藏
    DOI:10.4065/82.8.933 复制DOI
    作者列表:Gerber Y,Jacobsen SJ,Killian JM,Weston SA,Roger VL
    BACKGROUND & AIMS: OBJECTIVE:To compare the characteristics and survival of participants and nonparticipants in a community-based study of myocardial infarction (MI). PARTICIPANTS AND METHODS:Residents of Olmsted County, MN, who presented with elevated cardiac troponin T levels from September 1, 2002, through December 31, 2005, were prospectively enrolled and classified with standardized criteria for MI. With specific Institutional Review Board approval, the medical records of patients with MI who did not provide consent but who had given general research authorization were reviewed, as was done for their consenting peers. RESULTS:During the study period, 2277 individuals with elevated cardiac troponin T levels were approached, of whom 1863 (82 percent) consented to participate. Among the 414 nonparticipants, 375 (91 percent) had general research authorization. Of the 558 with general research authorization who met the criteria for incident (ie, first-ever) MI, 67 (12 percent) refused to participate. These participants tended to be older (mean plus or minus SD age, 71 plus or minus 14 vs 67 plus or minus 15 years; P equals .04), were more likely to be of races other than white (9 percent vs 2 percent; P equals .01), and had more comorbidities, including peripheral vascular disease (P equals .02), chronic pulmonary disease (P equals .06), heart failure (P equals .07), and impaired creatinine clearance (P equals .02). No significant differences were detected in cardiovascular risk factors or MI characteristics. During a median follow-up of 517 days, nonparticipants experienced increased mortality rates compared with participants (hazard ratio, 1.97; 95 percent confidence interval, 1.21 to 3.20), which was largely attributable to their older age and excess comorbidities (adjusted hazard ratio, 1.43; 95 percent confidence interval, 0.86 to 2.35). CONCLUSION:In this community-based study of MI, nonparticipants experienced worse survival rates than participants largely because of differences in demographic and clinical characteristics. These differences should be kept in mind when interpreting study results, particularly if participation is low.
    背景与目标:
  • 【在系统评价中用于识别和探索偏倚的定量方法的应用: 勃起功能障碍的PDE-5抑制剂。】 复制标题 收藏 收藏
    DOI:10.1038/sj.ijir.3901626 复制DOI
    作者列表:Bekkering GE,Abou-Setta AM,Kleijnen J
    BACKGROUND & AIMS: :A systematic review of PDE-5 inhibitors for erectile dysfunction was performed to evaluate the utility of quantitative methods for identifying and exploring the influence of bias and study quality on pooled outcomes from meta-analyses. We included 123 randomized controlled trials (RCTs). Methodological quality was poorly reported. All three drugs appeared highly effective. Indirect adjusted analyses showed no differences between the three drugs. Funnel plots and statistical tests showed no evidence of small-study effects for sildenafil whereas there was evidence of such bias for tadalafil and vardenafil. Adjustment for missing studies using trim and fill techniques did not alter the pooled estimates substantially. The exclusion of previous sildenafil nonresponders was associated with larger treatment effects for tadalafil. This investigation was hampered by poor reporting of methodological quality, a low number of studies, heterogeneity and large effect sizes. Despite such limitations, a comprehensive assessment of biases should be a routine in systematic reviews.
    背景与目标: : 对勃起功能障碍的PDE-5抑制剂进行了系统评价,以评估定量方法在鉴定和探索偏倚和研究质量对荟萃分析汇总结果的影响方面的实用性。我们纳入了123随机对照试验 (RCTs)。方法学质量报道不佳。这三种药物都非常有效。间接校正分析显示三种药物之间没有差异。漏斗图和统计测试没有证据表明西地那非的小研究效果,而有证据表明他达拉非和伐地那非存在这种偏倚。使用trim和fill技术对缺失研究进行的调整不会显着改变汇总的估计值。排除先前的西地那非无反应者与他达拉非更大的治疗效果相关。这项研究受到方法质量报告不佳,研究数量少,异质性和大效应大小的阻碍。尽管有这些限制,但对偏见的全面评估应该是系统审查的常规。
  • 【新型冠状病毒肺炎和怀孕: 纠正历史性性别偏见的机会。】 复制标题 收藏 收藏
    DOI:10.1002/jmv.26350 复制DOI
    作者列表:Comas C,Carreras E
    BACKGROUND & AIMS: :Current literature and clinical guidelines do not include pregnant women as an a priori risk group for COVID-19. However, a gender vision of health begs the question: Why are pregnant women not considered a risk group for COVID-19? The answer is clear: historically, most community scientific studies have not considered female gender, or pregnancy as a state, to be a focus of special interest or effort. Unfortunately, this bias seems to be maintained in the COVID-19 epidemic: most current guidelines for diagnosing SARS-CoV-2 infection during pregnancy apply the same standard criteria as for the general population. This pandemic is an opportunity to begin redressing this historic gender bias against pregnant women, and to achieve this, we recommend two actions that are easy to implement, and would have a large impact. First, routinely test for SARS-CoV-2 infection in all pregnant women with clinical or epidemiological suspicion, regardless of gestational age or the clinical severity. Second, routinely test for SARS-CoV-2 infection in all pregnant women at admission for delivery. These actions are essential to understand the true impact of COVID-19 throughout pregnancy, and will improve how we manage many aspects of pre- and postnatal care. It is the scientific community's responsibility to guide, even to anticipate, the recommendations of our respective governments' health policies. If we do not agree to consider pregnant women as a distinct priority subgroup of the population during this pandemic, once again we will miss an opportunity to overcome this historic bias.
    背景与目标: : 目前的文献和临床指南没有将孕妇作为新型冠状病毒肺炎的先验风险人群。然而,性别对健康的看法回避了一个问题: 为什么孕妇不被认为新型冠状病毒肺炎的风险群体?答案很明确: 从历史上看,大多数社区科学研究都没有将女性性别或怀孕视为一种状态,作为特别感兴趣或努力的重点。不幸的是,这种偏见似乎在COVID-19流行病中得以维持: 目前大多数诊断怀孕期间SARS-CoV-2感染的指南都采用与普通人群相同的标准。这场大流行是一个机会,可以开始纠正这种针对孕妇的历史性性别偏见,为了实现这一目标,我们建议采取两项易于实施并产生重大影响的行动。首先,对所有有临床或流行病学怀疑的孕妇进行常规SARS-CoV-2感染检测,无论胎龄或临床严重程度如何。第二,在所有孕妇入院分娩时常规检测SARS-CoV-2感染情况。这些行动对于了解新型冠状病毒肺炎在整个怀孕期间的真正影响至关重要,并将改善我们如何管理产前和产后护理的许多方面。科学界有责任指导甚至预测我们各自政府卫生政策的建议。如果我们不同意在这场大流行期间将孕妇视为人口中的一个独特的优先群体,我们将再次错过克服这一历史性偏见的机会。
  • 【妊娠期体重增加测量中的偏差最小化。】 复制标题 收藏 收藏
    DOI:10.1111/obr.13056 复制DOI
    作者列表:Stamm R,Coppell K,Paterson H
    BACKGROUND & AIMS: :Gestational weight gain (GWG) is an important predictor of adverse pregnancy outcomes including gestational diabetes, preterm birth, delivery by caesarean and post-partum weight retention. The Institute of Medicine guidelines on GWG are widely adopted, and GWG is widely researched as an outcome of interest in lifestyle interventions during pregnancy. However, estimation of prepregnancy weight and measurement of weight prior to delivery introduce bias into measures of GWG. This review discusses the sources of bias in measures of GWG and the potential effect of bias on the relationship between adverse pregnancy outcomes associated with GWG. Bias in measures of GWG can be minimized by using measured weight at the first antenatal appointment in early pregnancy rather than self-reported prepregnancy weight and by adjusting for gestational age when the last weight is collected earlier than the delivery date. Bias owing to gestational age is an important potential confounder in the relationship between GWG and adverse pregnancy outcomes.
    背景与目标: : 妊娠体重增加 (GWG) 是不良妊娠结局的重要预测指标,包括妊娠糖尿病,早产,剖腹产和产后体重保持。医学研究所关于GWG的指南被广泛采用,并且GWG被广泛研究,这是对怀孕期间生活方式干预的兴趣的结果。但是,孕前体重的估计和分娩前体重的测量将偏差引入了GWG的测量中。这篇综述讨论了GWG测量中偏倚的来源以及偏倚对与GWG相关的不良妊娠结局之间关系的潜在影响。通过在怀孕初期首次产前预约时使用测量的体重,而不是自我报告的孕前体重,以及在分娩日期之前收集最后一次体重时调整胎龄,可以最大程度地减少GWG测量的偏差。由于胎龄引起的偏见是GWG与不良妊娠结局之间关系的重要潜在混杂因素。
  • 【描述基于现场的公民科学家行为的数据衍生指标为项目设计和建模偏差提供了见解。】 复制标题 收藏 收藏
    DOI:10.1038/s41598-020-67658-3 复制DOI
    作者列表:August T,Fox R,Roy DB,Pocock MJO
    BACKGROUND & AIMS: :Around the world volunteers and non-professionals collect data as part of environmental citizen science projects, collecting wildlife observations, measures of water quality and much more. However, where projects allow flexibility in how, where, and when data are collected there will be variation in the behaviour of participants which results in biases in the datasets collected. We develop a method to quantify this behavioural variation, describing the key drivers and providing a tool to account for biases in models that use these data. We used a suite of metrics to describe the temporal and spatial behaviour of participants, as well as variation in the data they collected. These were applied to 5,268 users of the iRecord Butterflies mobile phone app, a multi-species environmental citizen science project. In contrast to previous studies, after removing transient participants (those active on few days and who contribute few records), we do not find evidence of clustering of participants; instead, participants fall along four continuous axes that describe variation in participants' behaviour: recording intensity, spatial extent, recording potential and rarity recording. Our results support a move away from labelling participants as belonging to one behavioural group or another in favour of placing them along axes of participant behaviour that better represent the continuous variation between individuals. Understanding participant behaviour could support better use of the data, by accounting for biases in the data collection process.
    背景与目标: : 作为环境公民科学项目的一部分,世界各地的志愿者和非专业人士收集数据,收集野生动植物观察,水质测量等。但是,如果项目允许灵活地收集数据的方式,地点和时间,则参与者的行为会有所不同,从而导致收集的数据集存在偏差。我们开发了一种量化这种行为变化的方法,描述了关键驱动因素,并提供了一种工具来解决使用这些数据的模型中的偏差。我们使用了一套指标来描述参与者的时间和空间行为,以及他们收集的数据的变化。这些被应用于多物种环境公民科学项目iRecord蝴蝶手机应用程序的5,268用户。与以前的研究相反,在删除了短暂的参与者 (那些在几天内活跃并且贡献很少的记录的参与者) 之后,我们没有发现参与者聚集的证据; 相反,参与者沿着四个连续的轴下降,这些轴描述了参与者行为的变化: 记录强度,空间范围,记录潜力和稀有记录。我们的结果支持将参与者标记为一个或另一个行为群体,而将其置于参与者行为的轴上,以更好地代表个体之间的连续变化。通过考虑数据收集过程中的偏差,了解参与者的行为可以支持更好地使用数据。
  • 【用于下一代测序的超灵敏扩增子条形码可促进序列错误和扩增偏倚校正。】 复制标题 收藏 收藏
    DOI:10.1038/s41598-020-67290-1 复制DOI
    作者列表:Ahmed I,Tucci FA,Aflalo A,Smith KGC,Bashford-Rogers RJM
    BACKGROUND & AIMS: :The ability to accurately characterize DNA variant proportions using PCR amplification is key to many genetic studies, including studying tumor heterogeneity, 16S microbiome, viral and immune receptor sequencing. We develop a novel generalizable ultrasensitive amplicon barcoding approach that significantly reduces the inflation/deflation of DNA variant proportions due to PCR amplification biases and sequencing errors. This method was applied to immune receptor sequencing, where it significantly improves the quality and estimation of diversity of the resulting library.
    背景与目标: : 使用PCR扩增准确表征DNA变异比例的能力是许多遗传研究的关键,包括研究肿瘤异质性,16s微生物组,病毒和免疫受体测序。我们开发了一种新型的可推广的超灵敏扩增子条形码编码方法,该方法可显着减少由于PCR扩增偏差和测序错误而导致的DNA变体比例的膨胀/收缩。该方法应用于免疫受体测序,可显着提高所得文库的质量和多样性估计。
  • 13 Context matters for attractiveness bias. 复制标题 收藏 收藏

    【语境对吸引力偏见很重要。】 复制标题 收藏 收藏
    DOI:10.1017/S0140525X16000546 复制DOI
    作者列表:Lee J,Adams G,Li YJ,Gillath O
    BACKGROUND & AIMS: :To fully understand the attractiveness bias, we propose that contextual factors or affordances should be integrated into the mating-based evolutionary account of Maestripieri et al. We review examples highlighting the role of contextual factors in the perception of attractiveness and in attractiveness bias. These suggest contextual factors differentially afford the development of preference for attractive others into observed habits of mind.
    背景与目标: : 为了充分理解吸引力偏差,我们建议将情境因素或承受能力整合到maestribieri等人基于交配的进化论中。我们回顾了一些例子,突出了情境因素在吸引力感知和吸引力偏差中的作用。这些表明上下文因素不同地使对有吸引力的他人的偏好发展成为观察到的思维习惯。
  • 【连续检验规范中的偏差-方差权衡。】 复制标题 收藏 收藏
    DOI:10.1177/1073191120939155 复制DOI
    作者列表:Voncken L,Albers CJ,Timmerman ME
    BACKGROUND & AIMS: :In continuous test norming, the test score distribution is estimated as a continuous function of predictor(s). A flexible approach for norm estimation is the use of generalized additive models for location, scale, and shape. It is unknown how sensitive their estimates are to model flexibility and sample size. Generally, a flexible model that fits at the population level has smaller bias than its restricted nonfitting version, yet it has larger sampling variability. We investigated how model flexibility relates to bias, variance, and total variability in estimates of normalized z scores under empirically relevant conditions, involving the skew Student t and normal distributions as population distributions. We considered both transversal and longitudinal assumption violations. We found that models with too strict distributional assumptions yield biased estimates, whereas too flexible models yield increased variance. The skew Student t distribution, unlike the Box-Cox Power Exponential distribution, appeared problematic to estimate for normally distributed data. Recommendations for empirical norming practice are provided.
    背景与目标: : 在连续测试规范中,测试分数分布被估计为预测因子的连续函数。一种灵活的范数估计方法是将广义加性模型用于位置,比例和形状。未知他们的估计对模型灵活性和样本量有多敏感。通常,适合总体水平的灵活模型比其受限的非拟合版本具有较小的偏差,但其采样变异性更大。我们研究了在与经验相关的条件下,模型的灵活性与归一化z分数的估计中的偏差,方差和总变异性之间的关系,其中涉及倾斜学生t和正态分布作为总体分布。我们考虑了横向和纵向假设的违反。我们发现,分布假设过于严格的模型会产生有偏差的估计,而过于灵活的模型会产生增加的方差。与Box-Cox幂指数分布不同,倾斜学生t分布似乎难以估计正态分布数据。提供了经验规范实践的建议。
  • 【Mls-1识别的MHC偏倚不受胸腺阳性选择的影响。】 复制标题 收藏 收藏
    DOI:10.1006/cimm.1996.0030 复制DOI
    作者列表:Nguyen P,Woodland DL,Blackman MA
    BACKGROUND & AIMS: In contrast to T cell recognition of conventional peptide/MHC, T cell recognition of superantigen is not MHC-restricted. However, an influence of MHC polymorphism on specificity is consistent with accumulating data suggesting a TCR/MHC interaction during T cell recognition of superantigen. We have previously shown that T cells from V beta 8.1 beta-chain transgenic mice show an unexpected bias against recognition of Mls-1 presented by H-2d spleen cells. In the current studies we have examined whether thymic positive selection in H-2d mice, which selects T cells that see conventional antigen preferentially in the context of H-2d, is able to overcome the strong bias against recognition of Mls-1/H-2d. The data show that transgenic T cells from both H-2d and H-2k mice have comparable reactivity. The failure of thymic positive selection to overcome the bias against Mls-1/H-2d suggests that the orientation of the putative TCR/MHC interaction during recognition of Mls-1 is not the same as during recognition of conventional peptide/MHC.

    背景与目标: 与常规肽/MHC的T细胞识别相反,超抗原的T细胞识别不受MHC限制。然而,MHC多态性对特异性的影响与积累的数据一致,这些数据表明在T细胞识别超抗原期间存在TCR/MHC相互作用。我们先前已经表明,来自V β 8.1 β 链转基因小鼠的T细胞显示出对H-2d脾细胞呈现的Mls-1识别的意外偏倚。在当前的研究中,我们检查了H-2d小鼠中的胸腺阳性选择是否能够克服对Mls-1/H-2d识别的强烈偏见,该选择在H-2d的背景下优先看到常规抗原的T细胞。数据显示来自H-2d和H-2k小鼠的转基因T细胞具有相当的反应性。胸腺阳性选择未能克服对Mls-1/H-2d的偏见,这表明在识别Mls-1过程中假定的TCR/MHC相互作用的方向与在识别常规肽/MHC过程中不同。

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