Methods for Quantitative Risk Assessment Using Occupational Studies

Although carcinogenic risk assessment is frequently based on animal bioassay data, occupational studies are generally considered the best source of data for quantitative risk estimation. The model selected for use with occupational study data is required to extrapolate on age, exposure level, and temporal exposure pattern. Relative and absolute risk models are examined, as are alternatives for the definition of a dose (exposure) variable. The models express disease incidence as a function of the chosen exposure variable and convert incidence into estimates of lifetime risk. In this form, predictions of the models can be compared. The methods are illustrated using three examples: arsenic exposure and respiratory cancer, leukemia associated with benzene exposure, and asbestos-induced mesothelioma.     

Estimation of Survivorship Function Based on Doubly Censored Data with Application to HIV/AIDS

Left censoring concept has been defined in different ways in statistical applications. Turnbull (1974 Turnbull , B. W. ( 1974 ). Nonparametric estimation of a survivorship function with doubly censored data . J. Amer. Statist. Assoc. 69 : 169 – 173 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) defines it in a particular way. Whereas in recent literature, especially in epidemiological studies, it has been defined in another way. This difference between the two approaches is the main reason that despite simplicity, Turnbull method cannot be applicable in all cases of doubly censored data. In this article we present a modified Turnbull method for analysis of doubly censored data adequate with recent definition. Comparison has been done with other statistical methods, including imputation estimator, full likelihood-based and conditional likelihood-based approach using Iranian HIV data.     

Data and projections of HIV/AIDS cases in Portugal: an unstoppable epidemic?

The size of the affected population with HIV/AIDS is a vital question asked by healthcare providers. A statistical procedure called Back-calculation has been the most widely used method to answer that question. Recent discussions suggest that this method is gradually becoming less appropriate for reliable incidence and prevalence estimates, as it does not take into account the effect of treatment. In spite of this, in the current paper that method and a worst-case scenario are used to assess the quality of previous projections and obtain new ones. The first problem faced was the need to account for reporting delays, no reporting and underreporting. The adjusted AIDS incidence data were then used to obtain lower bounds on the size of the AIDS epidemic, using the back-calculation methodology. A Weibull and Gamma distribution was considered for the latency period distribution. The EM algorithm was applied to obtain maximum likelihood estimates of the HIV incidence. The density of infection times was parameterized as a step function. The methodology is applied to AIDS incidence in Portugal for four different transmission categories (injecting drug users, heterosexual, homo/bisexual and other) to obtain short-term projections (2002–2005) and an estimate of the minimum size of the epidemic.     

Data and projections of HIV and AIDS in Portugal

Projections of AIDS incidence are critical for assessing future healthcare needs. This paper focuses on the method of back-calculation for obtaining forecasts. The first problem faced was the need to account for delays and underreporting in reporting of cases and to adjust the incidence data. The method used to estimate the reporting delay distribution is based on Poisson regression and involves cross-classifying each reported case by calendar time of diagnosis and reporting delay. The adjusted AIDS incidence data are then used to obtain short-term projections and lower bounds on the size of the AIDS epidemic. The estimation procedure 'back-calculates' from AIDS incidence data using the incubation period distribution to obtain estimates of the numbers previously infected. These numbers are then projected forward. The problem can be shown to reduce to estimating the size of a multinomial population. The expectation-maximization (EM) algorithm is used to obtain maximum-likelihood estimates when the density of infection times is parametrized as a step function. The methodology is applied to AIDS incidence data in Portugal for four different transmission categories: injecting drug users, sexual transmission (homosexual/bisexual and heterosexual contact) and other, mainly haemophilia and blood transfusion related, to obtain short-term projections and an estimate of the minimum size of the epidemic.     

经济不确定性的量化测度研究：前沿进展与理论综述

测量经济不确定性是一件重要但又较困难的事情,目前国内外专门研究经济不确定性测量方法的文献并不多。本文梳理了近年来国内外量化测度经济不确定性的文献,从中将零碎的有关经济不确定性的测量方法提炼出来,归纳为三大类：通过寻找合适的经济不确定性替代指标、通过调查数据计算被调查者对当前经济状况和预期的主观感知截面数据偏差（或预测偏差）计算不确定性、通过构建状态空间模型求解作为隐含状态量的经济不确定性。本文详细介绍了每类方法的原理和典型方法,对各类方法做了评述：分析了各类方法的适用场景和优缺点,探讨了应用每类方法的关键点和难点,并介绍了每类方法的代表性应用实例。本文清晰、全面地展示了目前量化测度经济不确定性的前沿进展和理论发展,为研究经济不确定性夯实基础工作,补缺了近年来国内在量化测度经济不确定性方法综述这一领域的空白。     

SAM平衡的SG-RAS与SG-CE方法

随机cross entropy(Robinson et al.,2001)方法是目前用于平衡社会核算矩阵的最主流方法,本文综合其与GRAS(Lenzen et al.,2007)方法的思想,扩展提出了SG-CE(stochastic generalized CE)与SG-RAS方法,避免了原始CE方法在平衡SAM时需要对负值元素进行预处理的步骤,试图改进由此引致的缺陷并提高平衡SAM质量。在此基础上,本文运用SG-RAS、SG-CE、CE以及国内常用的余量法对中国2007年SAM进行了平衡,实证结果的对比表明:在平衡系数SAM时,SG-RAS优势非常明显;而平衡流量SAM时,除SG-RAS之外,余量法也具较好表现;但无论是平衡系数还是流量SAM,SG-CE的效果只能说差强人意,原始CE方法更差。     

用Excel统计数值型数据频数分布的三种方法

本文根据两种不同的数据分组方式,分别讨论了利用Excel软件统计数值型数据频数分布的三种基本方法并作了简要评述。     

Models for residual time to AIDS

The distributions of the time from Human Immunodeficiency Virus (HIV) infection to the onset of Acquired Immune Deficiency Syndrome (AIDS) and of the residual time to AIDS diagnosis are important for modeling the growth of the AIDS epidemic and for predicting onset of the disease in an individual. Markers such as CD4 counts carry valuable information about disease progression and therefore about the two survival distributions. Building on the framework set out by Jewell and Kalbfleisch (1992), we study these two survival distributions based on stochastic models for the marker process (X(t)) and a marker-dependent hazard (h()). We examine various plausible CD4 marker processes and marker-dependent hazard functions for AIDS proposed in recent literature. For a random effects plus Brownian motion marker process X(t)=(a+bt+BM(t))⁴, where a has a normal distribution, b<0 is an unknown parameter and BM(t) is Brownian motion, and marker-dependent hazard h(X(t)), we prove that, given CD4 cell count X(t), the residual time to AIDS distribution does not depend on the time since infection t. Using simulation and numerical integration, we find the marginal incubation period distribution, the marginal hazard and the residual time distribution for several combinations of marker processes and marker-dependent hazards. An example using data from the Multicenter AIDS Cohort Study is given. A simple regression model relating the cube root of residual time to AIDS to CD4 count is suggested.     

权数对CPI的结果影响程度定量分析

权数是影响CPI精度的重要因素之一,通过对基本分类价格指数计算中的权数缺失和高层级价格指数计算中权数滞后的影响进行了理论和实证分析,结果表明,利用将销售量作为权数的联合比法对基本分类价格指数进行计算可以大幅提高其精度;高层级价格指数计算所用权数的滞后性同样会降低CPI的精度,且主要存在高估CPI的系统性误差问题。     

产业结构变化的评价方法探析

一、基本思路产业结构评价是统计评价的一个重要领域。在产业结构评价中,多数都是利用历史数据对产业结构的演变进行长期评价,而在众多的统计年度评价指数中,目前还缺乏对于产业结构年度变化的综合评价指数。国民经济产业结构每年都会发生变化,如果能找到一种综合评价产业结构年度变化合理性及程度的方法,对于政府及时调整产业政策就有一定的指导意义。描述和评价产业结构年度变化的合理性,其难点归纳起来主要有两个方面,一是短期评价的标准问题,二是如何综合成为一个指数。在一般分析中多数都用某一产业的比重上升或下降来说明问题,但综合…     

社会核算矩阵不同更新方法的比较研究

更新社会核算矩阵(Social Accounting Matrix, SAM)作为一种非调查技术一直受到普遍重视。本文用十种更新方法,包括RAS法、交叉熵法、广义交叉熵法等,以江苏省1997年的宏观和细化SAM为初始表,将其分别更新到2002年的宏观和细化SAM。我们通过保号检验、方向检验和接近程度检验比较了各种方法的更新结果。研究结论显示：第一,基于商的更新方法要优于基于距离的更新方法;第二,保号类方法不仅具有保号的功能,而且在方向检验和接近度检验中有着良好表现;第三,对某些重要系数采用适当的外生估算方式,可以提高SAM更新的精度。     

经济时间序列频率转换方法的研究与应用

经济时间序列的频率转换是计量经济分析领域的一个重要研究问题.本文首先对不同经济指标类型(流量、存量和指数)及传统频率转换方法进行了系统梳理;在此基础上,重点介绍了3种低频向高频转换的前沿方法:Denton方法、Chow-Lin方法和Litterman方法,并给出了流量、存量和指数3种类型变量由低频(季度)向高频(月度)转换的实例;最后,对3种频率转换方法的数据转换质量进行了比较分析.研究显示,频率转换后的月度数据都较好地反映季度数据的变化趋势和波动特征,从而通过频率转换方法可以很好地解决由于收集到的数据类型不一致而无法建模的问题.     

论统计理论研究方法体系

一、统计理论研究方法体系的提出　　在相当长的一段时间里,我国统计界在进行统计理论研究时虽有意无意地采用了一些研究方法,但是,这些研究方法基本上分散零乱的,没使之系统化,这也许是造成我国统计理论研究还比较落后的一个重要原因。随着市场经济的不断完善,统计理论研究的不断深入,人们发现我国统计理论研究在向新领域、新高度跨越时,现有的方法难以适应研究的需要,客观实际方面要求我们应不断地总结过去的研究方法,创建新的研究方法。因此,对统计理论研究方法本身的研究被提到议事日程。实际上,当今科学技术的飞跃进步,科…     

Imputation methods for doubly censored HIV data

In medical research, it is common to have doubly censored survival data: origin time and event time are both subject to censoring. In this paper, we review simple and probability-based methods that are used to impute interval censored origin time and compare the performance of these methods through extensive simulations in the one-sample problem, two-sample problem and Cox regression model problem. The use of a bootstrap procedure for inference is demonstrated.     

Imputation methods for doubly censored HIV data

In medical research, it is common to have doubly censored survival data: origin time and event time are both subject to censoring. In this paper, we review simple and probability-based methods that are used to impute interval censored origin time and compare the performance of these methods through extensive simulations in the one-sample problem, two-sample problem and Cox regression model problem. The use of a bootstrap procedure for inference is demonstrated.     

Likelihood Methods for Controlled Calibration

Abstract.  This paper presents the use of likelihood-based methods for controlled calibration. Recent results on higher-order asymptotics are exploited to obtain confidence regions for the output of the calibration process. A general likelihood-based approach is presented, and several types of calibration problems are tackled within this framework. The methods provide simple and accurate solutions which may have some potential usefulness for applications. The results are illustrated with reference to widely used models.     

Methods for projecting private households

"Although there exists a reasonable number of methods for projecting the number of private households, only a few of them are used in practice. The reason for this discrepancy is...analysed. All important methods which had been developed until now will be presented, focusing on their assumptions and the data needed." (SUMMARY IN ENG)     

Approximate Methods for State-Space Models

State-space models provide an important body of techniques for analyzing time-series, but their use requires estimating unobserved states. The optimal estimate of the state is its conditional expectation given the observation histories, and computing this expectation is hard when there are nonlinearities. Existing filtering methods, including sequential Monte Carlo, tend to be either inaccurate or slow. In this paper, we study a nonlinear filter for nonlinear/non-Gaussian state-space models, which uses Laplace's method, an asymptotic series expansion, to approximate the state's conditional mean and variance, together with a Gaussian conditional distribution. This Laplace-Gaussian filter (LGF) gives fast, recursive, deterministic state estimates, with an error which is set by the stochastic characteristics of the model and is, we show, stable over time. We illustrate the estimation ability of the LGF by applying it to the problem of neural decoding and compare it to sequential Monte Carlo both in simulations and with real data. We find that the LGF can deliver superior results in a small fraction of the computing time.