四种方法计算总体率可信区间的比较研究

目的 比较一次近似法、校正一次近似法、二次近似法和二项分布精确法计算总体率95％可信区间的精密度、可信度和相对误差，并探讨一次近似法和校正一次近似法的应用条件和注意事项。方法 用SAS软件编制Monte Carlo模拟抽样程序，比较4种方法的可信度；以精确法为标准，计算其他方法的精密度和相对误差。结果 校正一次近似法的可信度、精密度与精确法相似，相对误差明显小于一次近似法和二次近似法。二次近似法不论是可信度还是精密度均明显差于精确法，并具有显著的相对误差。结论 在进行率的区间估计时，建议采用校正一次近似法。     

单样本中位数可信区间估计

从某个总体中抽取一个随机样本 ,样本中位数就是总体中位数的点估计值 ,但点估计值不能告知所估计的未知总体中位数的可信程度。而总体中位数的区间估计则可以告知对估计的未知总体中位数的可信程度 ,即总体中位数落入可信区间的概率的大小。估计可信区间时 ,一般取显著性水平α =0 0 5或α =0 0 1,相应的可信系数为 1-α ,可信度为 10 0 (1-α) % ,通常按可信度估计可信区间。α =0 0 5和α =0 0 1是两个最常选用的α值 ,其相应的可信度为 95 %和 99%。也可根据所取α的不同 ,制定不同的可信度如 80 % ,85 %和 90 %等的可信区间。估计…     

正态近似法计算二项分布总体率95%可信区间的应用条件研究

目的对目前惯用的正态近似法计算总体率可信区间的应用条件进行评价,为正确应用该法提供理论基础和应用指导.方法应用二项分布原理计算总体率精确可信区间并与正态近似法计算结果相比较;采用蒙特卡洛模拟抽样评价可信度;应用SAS和Excel软件绘制二项分类数据概率分布图.结果以n×p=5作为近似条件,用正态近似法计算总体率可信区间可造成显著的相对误差.当n×p为常数时,随着p减小,相对误差在一定范围内呈线性增加;随着n增加,相对误差呈非线性增加.结论目前惯用的估计总体率可信区间的正态近似法应用条件并不能保证总体率估计的可信度和准确度.根据实验结果,提出了使用正态近似法估计总体率95%可信区间一套新的应用条件.     

PSU数量与入样比对抽样误差近似估计和统计推断影响

目的了解初级抽样单元(PSU)数量与入样比对抽样误差近似估计和统计推断的影响,为今后调查的抽样设计提供参考。方法收集2010年中国慢性病及其危险因素监测中的98 587条收缩压测量数据开展二阶段模拟抽样;采用泰勒级数线性化法估计每个样本在考虑有限总体校正(FPC)和不考虑FPC情况下的均值、标准误及95%可信区间,比较估计的标准误和真实标准误间差异,分析不同设计下95%可信区间包含总体均值参数的概率。结果 PSU个数增加至10个时,抽样误差迅速从4.13 mm Hg降到1.91 mm Hg,下降了53.8%,但PSU个数增加至≥20个时,估计精度未见明显提升;在考虑FPC情况下,随着PSU入样比的增加,均值95%可信区间覆盖真值的概率波动较大:入样比30%时,95%可信区间覆盖真值概率在94.0%上下波动;入样比30%时,95%可信区间覆盖真值的概率呈现出震荡下降的趋势,最低到达88.2%,统计推断较敏感;在不考虑FPC情况下,95%可信区间覆盖真值概率均较考虑FPC情况高,在PSU入样比20%时,95%可信区间覆盖真值概率较入样比20%时出现了一个小幅跃升,统计推断较保守。结论 PSU数量的确定需同时考虑估计精度和调查可行性;PSU入样比过大时,应慎重使用基于误差近似估计的统计推断。     

年龄调整率的区间估计及其在宫颈癌患病率估计中的应用

目的 评价三种年龄调整率可信区间估计方法,探索适合江苏省宫颈癌筛查研究中年龄调整患病率可信区间估计的方法.方法 以二项分布正态近似法、Gamma分布法及"确切概率法"进行年龄调整率的区间估计,运用统计模拟考察多种率及阳性数情况下三种方法的区间覆盖率及宽度.结果 当样本量较小(阳性数较少)时,确切概率法的覆盖率离理论可信度的偏差及区间宽度均优于Gamma分布法,两者的覆盖率均明显优于正态近似法;随着阳性数增多,三法各自的覆盖率偏差及区间宽度均逐渐变小,方法间的差异亦逐渐缩小;当阳性数增至30以上时,确切概率法及正态近似法的覆盖率的偏差皆在±1%以内,此时两者的区间宽度接近;而Gamma分布法的覆盖率偏差若要达到1%以内,则要求总阳性数在100以上.无论样本构成是轻度偏离还是明显偏离总体构成,上述规律皆成立.结论 综合考虑区间覆盖率、区间宽度及计算便捷性,建议当总阳性数小于30时,采用确切概率法计算调整率的可信区间;当总阳性数大于等于30时,采用正态近似法.     

我国18岁以上居民高血压患病率的区间估计

目的估计我国18岁以上居民的高血压患病率及其95%的可信区间。方法对复杂样本加权调整,使用SUDAAN 10.0.1软件,计算我国18岁以上居民的高血压患病率,并用泰勒级数法估计其方差和95%可信区间。结果我国18岁以上居民的高血压患病率及其95%可信区间为19.14%（18.15%～20.12%）,平均收缩压及其95%可信区间为120.0 mmHg（119.4～120.6 mmHg）,平均舒张压为76.4 mmHg,95%可信区间为76.0～76.8 mmHg。结论简单随机抽样的公式不适用于复杂抽样的数据点估计和区间估计值,应该根据具体的抽样设计来估计。同时,对复杂抽样数据进行抽样权重调整可以避免结果偏倚。     

诊断试验证实偏倚校正方法的比较研究

目的探讨两阶段两分类诊断试验存在证实偏倚时灵敏度和特异度的校正方法并进行比较。方法运用实例和模拟数据说明传统方法灵敏度和特异度的有偏估计,并运用最大似然估计和贝叶斯估计对灵敏度和特异度进行校正。结果传统方法计算的灵敏度和特异度存在偏倚,最大似然法和贝叶斯方法虽然均可校正估计偏倚,但是后者计算的可信区间比前者窄。结论在对诊断试验证实偏倚进行校正时,若有良好的先验信息,贝叶斯方法所获的结果更精确。     

关于可信区间的估计问题

问:在红细胞数抽样实验中,随机抽取 n=10的一个样本,求得(?)=488.6,s=61.65,95%可信区间为444.49～532.71,能不能说“有95%的把握估计μ是在444.49～532.71区间内”?答:95%是指概率而言,这里先要搞清楚什么是     

成本效果比五种可信区间估计法比较

目的给出成本效果比可信区间的最佳估计方法.方法采用理论探讨和实证研究比较盒法、Taylor级数法、椭圆法、Fieller's准则和非参Bootstrap法等5种计算增量成本效果比可信区间估计方法的优缺点.结果传统的统计学方法计算卫生经济学评价中增量成本效果比的可信区间会带来偏倚,Fieller's准则和非参数Bootstrap法的估计较为精确.结论推荐采用Bootstrap法估计增量成本效果比可信区间.     

REML法和Bayesian法对小样本不平衡单因素随机效应模型方差成分估计的模拟比较分析

目的 比较限制性极大似然估计(REML)法和贝叶斯法(Bayesian)对小样本不平衡单因素随机效应模型方差成分估计的偏差和精密度,同时考虑在样本量的大小、单位的数量和单位内相关系数(ICC)的大小不同的情况下对方差成分估计的精确程度的影响.方法 通过计算机模拟7组不同设计的数据集,用SAS软件MIXED模块进行方差成分估计.结果 不同的设计中,REML法估计比Bayesian法估计更加接近真值,但Bayesian法对组间方差的区间估计更加精密.对于两种方法 而言,样本和单位数量的增加,估计结果 更加准确.组内方差的估计,比组间方差的估计更准确和精密.结论 对小样本不平衡结构数据,当ICC为小或中等时,REML估计比Bayesian估计的偏差和均方误差要小,推荐使用.但是Bayesian法的区间估计比REML法的区间估计更加精密.     

Randomization inference for treatment effects on a binary outcome

Two methods are developed for constructing randomization‐based confidence sets for the average effect of a treatment on a binary outcome. The methods are nonparametric and require no assumptions about random sampling from a larger population. Both of the resulting 1 ? α confidence sets are exact in the sense that the probability of containing the true treatment effect is at least 1 ? α. Both types of confidence sets are also guaranteed to have width no greater than one. In contrast, a previously proposed asymptotic confidence interval is not exact and may have width greater than 1. The first approach combines Bonferroni‐adjusted prediction sets for the attributable effects in the treated and untreated. The second method entails inverting a permutation test. Simulations are presented comparing the two randomization‐based confidence sets with the asymptotic interval as well as the standard Wald confidence interval and a commonly used exact interval for the difference in binomial proportions. Results show for small to moderate sample sizes that the permutation confidence set attains the narrowest width on average among the methods that maintain nominal coverage. Extensions that allow for stratifying on categorical baseline covariates are also discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

老年泌尿系手术罗哌卡因腰麻最低运动阻滞浓度的研究

[目的]测定重比重罗哌卡因用于老年人泌尿系手术蛛网膜下腔阻滞麻醉的ED50。[方法]46例拟行泌尿系手术的老年人在蛛网膜下腔注射预设浓度的罗哌卡因。按序贯试验法设定罗哌卡因给药剂量,起始剂量为0.375%,浓度间隔为0.025%。用概率单位回归法计算ED50及其95%置信区间。[结果]罗哌卡因的ED50为0.325601%(95%置信区间为0.311089%～0.340789%)。[结论]泌尿系手术老年人腰硬联合麻醉需应用0.325%浓度的罗哌卡因可获得满足临床需要的感觉运动分离。     

The application of jackknife statistics to estimates of the recombination fraction

We develop and evaluate the jackknife statistics [Efron, 1982] for obtaining confidence intervals for the recombination fraction. We consider two cases: (1) a single sibship of size S with phase known parents (one doubly heterozygous and one doubly homozygous) and (2) a sample of 20 nuclear families. We compare the jackknife confidence interval to the ?1.00 lod and ?0.83 lod intervals. For the first case we compare our intervals with a confidence interval which we develop that has coverage of exactly 95%. For the second case, we do a simulation study and compare the coverage of the intervals and the endpoints of the intervals with the actual 2.5th and 97.5th percentiles. Our results indicate that in case (1) the lod intervals provide closer estimates to the 95% exact interval than does the jackknife approach. However, in case (2), although the lod intervals have better coverage probabilities, the jackknife interval endpoints are closer to the actual percentile points than either of the lod interval endpoints. © 1993 Wiley-Liss, Inc.     

工作场所空气中环氧丙烷热解吸气相色谱法测定的不确定度评定

目的建立工作场所空气中环氧丙烷热解吸气相色谱法测定的不确定度评定方法,通过控制这些因素提高检测结果的置信度和准确性。方法依据中华人民共和国国家计量技术规范JJF 1059-1999《测量不确定度评定与表示》进行评定。结果环氧丙烷不确定度主要来源:①标准状态下采样体积V0不确定度;②标准气体配制过程引入的不确定度;③工作曲线绘制方法引入的不确定度;④样品测定重复性引入的不确定度。取置信概率为95%,包含因子k=2,则其扩展不确定度:U=2×5.79%=11.58%。结论该不确定度评定方法对环氧丙烷的热解吸气相色谱法检测过程的质量控制意义十分重大,可以提高检测结果的准确性和置信度。     

2006年重庆市沙坪坝区学龄前儿童肥胖及其影响因素调查

[目的]了解重庆市沙坪坝区儿童肥胖发生状况及其影响因素，为制订预防和控制对策提供依据。[方法]2006年10月，对辖区内7307名3～6岁儿童进行调查，采用1：1配对分析查出的肥胖儿童与非肥胖儿童有关肥胖影响因素的OR值。[结果]调查7307名儿童，肥胖者134名，肥胖率为1．83％。肥胖率，男童为2．12％，女童为1．50％（P〈0．05）；3～6岁分别为1．70％、1．45％、1．38％、3．71％（P〈0．01）。肥胖儿童与非肥胖儿童相比，在喜欢食肉类、喜食甜食、进食量大、进食速度快、人工喂养、出生体重〉4000g、父母一方或双方肥胖者的OR值的95％可信限均大于1；户外活动、父母一方或双方为大专以上文化程度者的OR值的95％可信限均小于1。[结论]沙坪坝区3～6岁儿童肥胖率处于一般水平。不良饮食习惯与遗传是影响儿童肥胖的主要因素。     

Confidence intervals based on some weighting functions for the difference of two binomial proportions

In this paper, we propose two new methods for computing confidence intervals for the difference of two independent binomial proportions in small sample cases. Several test‐based exact confidence intervals have been developed to guarantee the nominal coverage probability in small sample cases. However, these methods are sometimes unnecessarily too conservative because they use the exact p‐value for constructing confidence intervals by maximizing the tail probability to account for the worst configuration. In order to reduce conservatism, our new methods adopt the p‐value weighted by two types of functions instead of the maximum p‐value. Our proposed methods can be regarded as quasi‐exact methods. The performance evaluation results showed that our methods are much less conservative than the exact method. Compared with other existing quasi‐exact methods, generally, our methods possess coverage probabilities closer to the nominal confidence level and shorter expected confidence widths. In particular, the beta weighing method provides the most reasonable balance between accurate coverage probability and short interval width in small sample cases. Copyright © 2014 John Wiley & Sons, Ltd.     

Confidence intervals for the binomial parameter: some new considerations

Several methods have been proposed to construct confidence intervals for the binomial parameter. Some recent papers introduced the "mean coverage" criterion to evaluate the performance of confidence intervals and suggested that exact methods, because of their conservatism, are less useful than asymptotic ones. In these studies, however, exact intervals were always represented by the Clopper-Pearson interval (C-P). Now we focus on Sterne's interval, which is also exact and known to be better than the C-P in the two-sided case. Introducing a computer intensive level-adjustment procedure which allows constructing intervals that are exact in terms of mean coverage, we demonstrate that Sterne's interval performs better than the best asymptotic intervals, even in the mean coverage context. Level adjustment improves the C-P as well, which, with an appropriate level adjustment, becomes equivalent to the mid-P interval. Finally we show that the asymptotic behaviour of the mid-P method is far poorer than is generally expected.     

Smoking and the occurrence of Alzheimer's disease: cross-sectional and longitudinal data in a population-based study

The authors tested the hypothesis that smoking exerts a protective effect on Alzheimer's disease or dementia in a population-based cohort of 668 people aged 75-101 years (Sweden). Smoking was negatively associated with prevalent Alzheimer's disease (adjusted odds ratio = 0.6, 95% confidence interval 0.4-1.1) and dementia (adjusted odds ratio = 0.6, 95% confidence interval 0.4-1.0). Over 3-year follow-up (1989-1992), the hazard ratios of incident Alzheimer's disease and dementia due to smoking were 1.1 (95% confidence interval 0.5-2.4) and 1.4 (95% confidence interval 0.8-2.7). Mortality over 5-year follow-up was greater among smokers in demented (hazard ratio = 3.4) than nondemented (hazard ratio = 0.8) subjects. Smoking does not seem protective against Alzheimer's disease or dementia, and the cross-sectional association might be due to differential mortality.     

Heroin use during methadone maintenance treatment: the importance of methadone dose and cocaine use.

OBJECTIVES. The purpose of this study was to examine factors associated with heroin use during methadone maintenance treatment. METHODS. Logistic regression statistical models were used to examine data obtained in a cross-sectional sample of 652 methadone patients. RESULTS. Heroin use during the 3 months prior to interview was shown to be greatest among (1) patients maintained on methadone dosages of less than 70 mg/day (adjusted odds ratio [OR] = 2.1, 95% confidence interval [CI] = 1.3, 3.4) and (2) patients who used cocaine during treatment (adjusted OR = 5.9, 95% CI = 3.8, 9.1). These results were independent of treatment duration, treatment compliance, alcohol use, and socioeconomic factors. Cocaine users were more likely than nonusers of cocaine to use heroin at all methadone dosage levels. CONCLUSIONS. This study confirms and extends past research showing high-dose methadone maintenance to be important to heroin abstinence. Further investigation of the independent association between heroin use and cocaine use is needed.