Concordance odds ratios and approximate rate ratios in longitudinal twin studies

Odds ratios derived from probandwise concordance rates are usually interpreted as increased risks in twins. Though the odds ratios in case–control studies have been shown to reflect rate ratios, few studies focused on such relationships in twin studies. The authors derived an approximate formula for the ratios of person-time incidence rates after the random assignment of twins into index twins and co-twins, i.e., incidence rate ratios. The resulting rate ratio was estimated as the product of the concordance odds ratio and a term that reflect the follow-up duration and the average time to occurrence of disease. Odds ratios coincide with rate ratios when the average time to occurrence of disease is half the duration of follow-up, although in studies spanning several decades these two measures might be different. The authors illustrated that when the incidence rate is not constant over the follow-up period as in longitudinal twin studies, the conventional odds ratio should not be used as an estimator of rate ratio.     

Comparison of methods for analyzing binary data arising from two-sample twin studies

The study of twins is widely used for research into genetic and environmental influences on human outcome measurements. For the study design in which independent samples of monozygotic and dizygotic twins are compared with respect to their similarity on a binary trait, several statistical methods have been proposed. Using a Monte Carlo simulation, we compare the five following procedures: 1) goodness-of-fit method based on the common correlation model, 2) normal approximation of the maximum likelihood estimators of the common correlation coefficients, 3) Ramakrishnan et al. [(1992) Genet Epidemiol 9:273–282] method of odds ratio comparison, 4) generalized estimating equations method of odds ratio estimation, and 5) tetrachoric correlation method. The results show that the goodness-of-fit approach has similar or better performance in both type-one error rates and power than the other methods in all parameter settings. Its advantage with respect to type-one error rates is particularly clear under conditions of small sample sizes, extreme prevalences, or high values of the intraclass correlation coefficients. Therefore, the goodness-of-fit method is recommended for the two-sample twin study design. Genet. Epidemiol. 14:349–363,1997. © 1997 Wiley-Liss, Inc.     

Further results on covariate measurement errors in cohort studies with time to response data

The impact of covariate measurement errors on the estimation of relative risk regression parameters is discussed. First the dependence of the induced relative risk process on the cumulative baseline failure rate function is noted. Next induced relative risk models under some specific failure time and measurement error models are described, including the much simplified models that are appropriate under a 'rare disease' assumption. The presentation then turns to the joint estimation of relative risk parameters of primary interest along with measurement error parameters. A partial likelihood product is proposed for such estimation and asymptotic properties are indicated. Guidance is also presented as to the appropriate size of a 'validation' sample relative to the full cohort size. Finally some more general considerations are presented as to the usefulness and interpretation of deattenuated regression coefficients.     

B-Lynch改良缝合法预防双胎妊娠剖宫产术后出血

目的探讨B-Lynch改良缝合法预防双胎妊娠剖宫产术后出血的临床效果。方法对双胎妊娠手术152例采用前瞻性观察方法,随机分为观察组（B-Lynch改良缝合组）76例和对照组（常规处理组）76例,观察两组术中出血量、术后24h出血量。结果观察组术中、术后24h出血量明显低于对照组,组间差异有统计学意义（P〈0.05）;观察组产后出血、产褥病发生率明显低于对照组,差异有统计学意义（P〈0.05）。结论 B-Lynch改良缝合法预防双胎妊娠剖宫产术后出血效果明显,值得临床推广。     

病例对照研究中logistic回归参数估计的应用条件研究

目的通过计算机模拟抽样,对病例对照研究资料logistic回归模型参数极大似然估计方法的应用条件进行探讨,为正确应用该法提供理论基础和应用指导.方法利用SAS函数抽取四格表资料,应用LogXact软件计算MLE及精确推断结果,对其进行比较.结果当暴露比低于0.1,尤其是OR比较大的情况下,MLE法必须满足大样本条件;随着暴露比的增加,MLE法对样本含量的要求可以放宽,暴露比为0.2,每组样本例数可为15例.结论MLE法估计logistic模型参数对样本含量的要求可以有条件的放宽;精确推断是MLE法的补充.     

logistic回归参数遗传算法估计的可行性研究

目的 考察遗传算法作为logistic回归模型参数估计方法的效能,并与极大似然估计法比较.方法 通过数据模拟建立三种模型,分别用遗传算法和极大似然法作参数估计,考察建立模型的分类效能.结果 一般情况下,极大似然估计法的分类效能稍高于遗传算法.在样本量较小或自变量关系复杂的情况下,极大似然估计法和遗传算法的泛化误差增加.极大似然估计法的泛化误差主要源于在验证集中分类效能下降,而遗传算法的泛化误差主要源于训练集中的过拟合.当样本量小且自变量关系复杂的情况下,极大似然估计法出现迭代不收敛,参数失拟合,遗传算法无此现象.结论 遗传算法适用于自变量多而样本量相对小时logistic回归模型参数估计.     

非线性因子分析模型参数估计研究

目的研究非线性因子分析模型的参数估计方法.方法利用MCECM算法对模型参数进行极大似然估计,利用Louis公式计算标准误.结果统计模拟结果显示估计值与真实值比较吻合,误差较小.结论基于MCECM算法的极大似然估计方法可用于估计非线性因子分析模型的参数.     

中国11省市35～64岁人群应用不同代谢综合征诊断标准的比较

目的比较美国国家胆固醇教育计划成人治疗方案第三次报告(NCEP-ATPⅢ)、国际糖尿病联盟(IDF)和中华医学会糖尿病学分会(CDS)建议的代谢综合征(MS)诊断标准在中国35～64岁人群中应用的差异。方法1992年对中国11省市35～64岁人群共29 564人进行了心血管病危险因素基线调查,1996—1999年又入选了35～64岁男女两性共3129人,分别应用三种标准计算该人群MS的患病率,分析不同标准时MS异常组分及危险因素聚集的检出情况,比较三种标准在中国人群中应用的一致性和差异。结果(1)应用ATPⅢ、IDF和CDS标准计算中国人群MS的年龄标化患病率分别为18.7%、14.6%和9.0%。(2)ATPⅢ诊断MS中有77.8%的人有中心性肥胖,22.2%无中心性肥胖;IDF诊断为非MS者中还有4.6%的人有3个及以上危险因素聚集;CDS诊断为非MS者中还有11.2%的人有3个及以上危险因素聚集。(3)ATPⅢ和IDF诊断标准在中国人群中应用的一致性较好,男女两性的Kappa值分别为0.795和0.899;CDS诊断标准与另两种诊断标准的一致性不高。(4)男性腰围切点为85 cm,女性腰围切点为80 cm时,预测危险因素聚集的ROC曲线距离分别为0.40和0.34,其在所选择的切点中ROC曲线距离相对最短。结论在三种MS诊断标准中,ATPⅢ诊断中国人群MS的患病率及检出危险因素聚集的比例最高;适宜中国人群的最佳腰围切点为男性85 cm、女性80 cm。     

A comparison of tests of homogeneity of odds ratios in K 2 x 2 tables

We conducted a simulation study to determine the performance of nine procedures for testing the homogeneity of odds ratios in K 2 x 2 contingency tables. We recommend Tarone's approximate score test, based on the Mantel-Haenszel estimator of the common odds ratio, for use in practice. We also recommend a non-iterative statistic developed by Gart and based on the modified Woolf estimator of the common odds ratio for very large samples in balanced or mildly unbalanced designs. We base our recommendation of a statistic on its performance in terms of size and power in comparison with the other statistics considered.     

双生子的血清脂质和脂蛋白遗传度及影响因素分析

目的　分析儿童、青少年的血脂指标遗传度及影响因素。方法　选择 5～ 19岁双生子2 36对 ,平均年龄 (11 2± 3 4 )岁 ,其中同卵双生子 14 3对 ,异卵双生子 93对。在DNA卵性鉴定基础上 ,以组内相关系数法及Falconer公式计算调整年龄性别前后的遗传度 ,偏态数据进行对数转换 ;校正年龄性别 ,分析相关体格、生化指标对血脂的影响。结果　同卵与异卵双生子间甘油三酯对内方差及相关系数的差异均无显著性 ;总胆固醇、高密度脂蛋白胆固醇 (HDL C)、低密度脂蛋白胆固醇 (LDL C)和脂蛋白 (a)对内方差及相关系数的差异有显著性 ,遗传度估计值分别为 0 5 6、0 5 5、0 4 9和 0 5 8,调整年龄性别后各指标估计遗传度分别为 0 6 3、0 6 3、0 5 5和 0 6 4。总胆固醇、HDL C、LDL C和脂蛋白(a)与年龄呈负相关 ;女孩的总胆固醇、HDL C、LDL C稍高于男孩。校正年龄性别后除脂蛋白 (a)外各血脂指标多数与体重指数、体脂率及培利迪西指数相关 ,与血压、血糖和血钙等也有相关性。结论　总胆固醇、HDL C、LDL C和脂蛋白 (a)受遗传因素影响较大 ,而甘油三酯主要受环境因素影响。儿童的血脂水平受年龄和性别的影响 ,与反映体脂和机体营养发育的指标相关。     

利用结构方程模型计算双生子一侧优势功能特征的遗传度

目的 分析遗传和环境因素分别对3项一侧优势功能特征的影响.方法 对在青岛市和丽水市两地募集的511对双生子进行一侧优势功能(利手、扣手、交叉臂方式)的判定,计算3项左型性状的一致率、卵别比值比、四项相关系数,并用openMx软件进行遗传模型的拟合.结果 左利手的最佳拟合为AE模型,遗传度为45.5％,左型扣手和左型交叉臂的最佳模型为DE模型,显性遗传效应分别是13.5％和6.1％.年龄和性别对遗传效应的影响无统计学意义.结论 左利手的遗传度为45.5％,扣手和交叉臂的遗传表现为显性遗传,但主要受环境影响.     

Use of death certificates in epidemiological studies, including occupational hazards: discordance with clinical and autopsy findings.

There has long been evidence of frequent inaccuracy of death certificates, with significant discordance between such designations and clinical and autopsy data. This exists for occupational diseases as well. The use of statistical rates based on death certificates has been seriously questioned despite their utility for total mortality. Programs to supplement death certificate data, particularly in occupational disease studies, may be helpful, and are reviewed.     

Interval estimation of the attributable risk in case-control studies with matched pairs

OBJECTIVE: The attributable risk (AR), which represents the proportion of cases who can be preventable when we completely eliminate a risk factor in a population, is the most commonly used epidemiological index to assess the impact of controlling a selected risk factor on community health. The goal of this paper is to develop and search for good interval estimators of the AR for case-control studies with matched pairs. METHODS: This paper considers five asymptotic interval estimators of the AR, including the interval estimator using Wald's statistic suggested elsewhere, the two interval estimators using the logarithmic transformations: log(x) and log(1-x), the interval estimator using the logit transformation log(x/(1-x)), and the interval estimator derived from a simple quadratic equation developed in this paper. This paper compares the finite sample performance of these five interval estimators by calculation of their coverage probability and average length in a variety of situations. RESULTS: This paper demonstrates that the interval estimator derived from the quadratic equation proposed here can not only consistently perform well with respect to the coverage probability, but also be more efficient than the interval estimator using Wald's statistic in almost all the situations considered here. This paper notes that although the interval estimator using the logarithmic transformation log(1-x) may also perform well with respect to the coverage probability, using this estimator is likely to be less efficient than the interval estimator using Wald's statistic. Finally, this paper notes that when both the underlying odds ratio (OR) and the prevalence of exposure (PE) in the case group are not large (OR < or =2 and PE < or =0.10), the application of the two interval estimators using the transformations log(x) and log(x/(1-x)) can be misleading. However, when both the underlying OR and PE in the case group are large (OR > or =4 and PE > or =0.50), the interval estimator using the logit transformation can actually outperform all the other estimators considered here in terms of efficiency. CONCLUSIONS: When there is no prior knowledge of the possible range for the underlying OR and PE, the interval estimator derived from the quadratic equation developed here for general use is recommended. When it is known that both the OR and PE in the case group are large (OR > or =4 and PE > or =0.50), it is recommended that the interval estimator using the logit transformation is used.     

患病人数未知时患病率的点估计及区间估计方法

目的研究患病人数未知时患病率的点估计及区间估计方法。方法根据概率论和数理统计原理导出患病率和阳性检出率、实验灵敏度、特异度间的定量关系,用代数推导和医学实例验证导出的公式。结果在已知实验灵敏度、特异度条件下,导出并验证了由阳性检出率计算患病率的点估计和区间估计方法。结论在患病人数未知条件下,使用阳性检出率和检验方法灵敏度、特异度等信息,可准确估计患病率,这一方法具有重要的公共卫生学意义。     

Bayesian and classical estimation of mixed logit: An application to genetic testing

Discrete choice experiments (DCEs) in health economics have recently used the mixed logit (MXL) model to incorporate preference heterogeneity. These studies typically use a classical approach to estimation or have specified normal distributions for the attributes. Specifying normal distributions can lead to erroneous interpretation; non-normal distributions may cause problems with convergence to the global maximum of the simulated log-likelihood function. Hierarchical Bayes (HB) of MXL is an alternative estimation approach that may alleviate problems of convergence. We investigated Bayesian and classical approaches to MXL estimation using a DCE that elicited preferences for a genetic technology. The classical approach produced unrealistic results in one of the econometric specifications, which led to an erroneous willingness to pay estimate. The HB procedure produced reasonable results for both specifications and helped ascertain that the classical procedures were converging at a local maximum.     

Outcomes of medical abortion through 63 days in women with twin gestations

Background

Twin gestation is not considered a contraindication to medical abortion with mifepristone and misoprostol. However, data comparing the efficacy of medical abortion for singleton gestations as compared with multiple gestations are limited. We examined medical abortion outcomes for twin gestations through 63 days.

Study Design

We performed a secondary analysis of treatment efficacy and side effects using pooled data from two randomized medical abortion trials. All subjects received mifepristone 200 mg orally and misoprostol 800 mcg vaginally. Outcomes in women with singleton and twin gestations were compared.

Results

Of 2208 subjects, 24 (1.1%) women had twins. Treatment success was not statistically different for twin and singleton gestations (91% vs. 97%, p=.19). Perceived bleeding and pain were not significantly different between groups.

Conclusions

Treatment success of medical abortion for twins is not significantly different than for singletons, although small differences cannot be excluded due to the limited number of twins.     

Use of death certificates in epidemiological studies, including occupational hazards: variations in discordance of different asbestos-associated diseases on best evidence ascertainment.

There is extensive information on discordance in general between accuracy of medical diagnoses on death certificate categorization of cause of death and available clinical and histopathological data. This is as true for occupational disease as for other conditions. But occupational illnesses bear a special problem. Discordance is not equal across the board--it may vary with each occupationally related disease, and no single formula can be applied. It may be high for angiosarcoma and low for acute hydrogen sulfide poisoning, low for bladder cancer, high for unsuspected methyl mercury poisoning. We have found that for one agent--asbestos--there were different rates of discordance for different asbestos-related diseases (e.g., lung cancer, mesothelioma, asbestosis, kidney cancer) among 4,951 deaths studied prospectively from 1967 to 1986. Caution is therefore required before accepting generalizations concerning (unstudied) discordance in occupational mortality studies, and in their use in risk assessment models.     

广东省居民低血压流行病学特征分析

目的　分析广东省居民低血压流行病学特征。方法　采用多阶段分层整群随机抽样方法 ,抽取新兴县、广州市越秀区等 1 3个市 (县、区 ) ,所有抽中家庭的 1 5岁及以上人口作为调查对象。被调查对象收缩压 (SBP)≤ 98mmHg并且舒张压 (DBP)≤ 6 0mmHg为低血压。采用 1 990年全国人口普查数据进行标化 ,并与 1 991年高血压调查数据进行比较。结果　共调查 1 5 4 74人 ,1 5岁及以上居民低血压粗患病率为 4 0 % ,其中男性为 2 4 % ,女性为 5 2 % ,女性高于男性 (χ2 =87 4 7,P <0 0 1 ) ;标化患病率为 5 7% ,其中男性为 3 4 % ,女性为 7 3% ,女性高于男性 (Z =1 4 72 ,P <0 0 1 )。随着年龄的增加 ,男女性低血压的患病率均呈下降趋势 (趋势 χ男2 =1 5 9 2 6 ,χ女2 =1 78 0 0 ,χ总2 =31 7 96 ,P值均 <0 0 1 ) ;低血压患病率随文化程度、工作种类的改善而升高 ;农村患病率较城市高 ;单身者较有配偶者患病率高。与 1 991年相比 ,2 0 0 2年广东省居民低血压的标化患病率降低 (Z =2 98,P <0 0 1 ) ,女性除 1 5～岁年龄组外 ,其他年龄组低血压患病率均降低 ,男性低血压患病率除 1 5～岁年龄组升高外 ,其他年龄组无变化。结论　广东省低血压患病率在不同人群的分布相差较大 ,低年龄、女性、高文化程度、国     

体外受精-胚胎移植术后双胎妊娠之一发育停止后存留胎儿的妊娠结局

目的探讨体外受精～胚胎移植术（IVF-ET）后宫内双胎妊娠之一发育停止后存留胎儿的妊娠结局。方法对2004年1月—之012年6月在本科室行IVF-ET、单精子卵胞浆内注射术（ICSI）后获得妊娠的临床资料进行回顾性分析,比较IVF-ET、ICSI术后双胎妊娠存留胎儿（另一胎儿在孕早期,≤12周或孕中晚期,〉12周发育停止）与同期IVF-ET术后单胎妊娠的妊娠结局。结果宫内双胎妊娠之一〉12周发育停止组分娩孕周和新生儿出生体重[（36．3±1．8）周、（2656．3±664．6）g],双胎妊娠组分娩孕周、新生儿体重、早产和低体重儿发生率[（35．1±2．4）周、（2515．8±493．6）g、50．9％、28．2％],双胎妊娠之一〉12周发育停止组早产、低体重儿发生率和新生儿死亡率（30．9％、21．8％、3．6％）,与单胎妊娠组比较,差异有统计学意义。结论IVF-ET后双胎妊娠之一在孕中晚期（〉12周）发育停止后存留胎儿的妊娠结局较单胎妊娠差。     

11省市队列人群代谢综合征的流行病学研究

目的　探讨队列人群代谢综合征的流行病学特征。方法　在 1992年对 11省市队列人群 (35～ 6 4岁 ) 2 7739人进行基线危险因素的调查。计算队列人群代谢综合征患者各种因素的均值±标准差和标化患病率。结果　 (1) 11省市队列人群有代谢综合征者高腰围的百分率最高 ,男性为89 0 % ,女性为 85 1%。其他主要指标 (除高密度脂蛋白 )男性均高于女性 ;(2 )代谢综合征患病率为13 3% ,其中男性为 12 7% ,女性为 14 2 % ,且随年龄的增加而增长 ;(3)多元logistic分析结果表明 ,腰围和糖尿病家族史是男性代谢综合征患者的危险因素 ,女性为腰围和高血压家族史。高密度脂蛋白增高是代谢综合征的保护因素。结论　 11省市队列人群代谢综合征患病率较高 ,腰围增大是代谢综合征重要的危险因素。