Estimation of Benchmark Dose of Lifetime Cadmium Intake for Adverse Renal Effects Using Hybrid Approach in Inhabitants of an Environmentally Exposed River Basin in Japan

The aim of this study is to estimate the reference level of lifetime cadmium intake (LCd) as the benchmark doses (BMDs) and their 95% lower confidence limits (BMDLs) for various renal effects by applying a hybrid approach. The participants comprised 3,013 (1,362 men and 1,651 women) and 278 (129 men and 149 women) inhabitants of the Cd‐polluted and nonpolluted areas, respectively, in the environmentally exposed Kakehashi River basin. Glucose, protein, aminonitrogen, metallothionein, and β₂‐microglobulin in urine were measured as indicators of renal dysfunction. The BMD and BMDL that corresponded to an additional risk of 5% were calculated with background risk at zero exposure set at 5%. The obtained BMDLs of LCd were 3.7 g (glucose), 3.2 g (protein), 3.7 g (aminonitrogen), 1.7 g (metallothionein), and 1.8 g (β₂‐microglobulin) in men and 2.9 g (glucose), 2.5 g (protein), 2.0 g (aminonitrogen), 1.6 g (metallothionein), and 1.3 g (β₂‐microglobulin) in women. The lowest BMDL was 1.7 g (metallothionein) and 1.3 g (β₂‐microglobulin) in men and women, respectively. The lowest BMDL of LCd (1.3 g) was somewhat lower than the representative threshold LCd (2.0 g) calculated in the previous studies. The obtained BMDLs may contribute to further discussion on the health risk assessment of cadmium exposure.     

Labor market competitiveness and the size of the informal sector

This paper formalizes the dynamics of the informal sector with a special emphasis on the levels of labor market competitiveness in the formal and informal sectors. Specifically, it analyzes the effects of improved productivity and higher entry costs into the formal sector on the size of the informal sector for different degrees of competitiveness in the labor markets. We show that when the informal labor market is competitive while the formal labor market is not, lower production technology in the formal sector or a higher entry cost reduces the size of the informal sector in the long run.     

Cumulants of random sum distributions

Consider a random variable S being the sum of a number N of independent and identically distributed random variables X_j (j = 1, 2, ...) where the number N is itself a non-negative integer-valued random variable independent of the X_j An explicit expression of the r-th cumulant of S is given in terms of the cumulants of N and X_j, Asymptotic properties of the distribution of S are also discussed.     

Recurrence formula on the joint distribution of sample skewness and kurtosis under normality

Abstract

Two recurrence relations with respect to sample size are given concerning the joint distribution of skewness and kurtosis of random observations from a normal population: one between the probability density functions and the other between the product moments. As a consequence, the latter yields a recurrence formula for the moments of sample kurtosis. The exact moments of Jarque-Bera statistic is also given.     

日本对外经济政策的演变(上)——从日美产业结构调整磋商到东亚共同体构想的提出

20世纪90年代,日本对外经济政策经历了两个方面的模式转变:第一,在贸易摩擦的应对和处理方面,摆脱了以往重视双边磋商和达成妥协的作法,转向通过多边框架以法律途径解决争端的轨道;第二,在贸易与投资自由化的促进方面,从多边主义转向了区域主义和双边主义。本文主要探讨导致这一模式转变的原因、模式转变过程中的促进势力和抵制势力以及抵制势力被克服的政策形成过程、两个模式之间的矛盾与冲突以及模式转变的稳定性等问题,在此基础上分析和展望日本今后的对外经济政策走向。     

Social norms, inequality and child labor

This paper theoretically analyzes a situation wherein adults’ decisions on child labor are affected not only by materialistic utility but also by a social norm against child labor. The adult thus faces a tradeoff; on the one hand, household income rises if she sends her child to work. On the other hand, the adult suffers disutility from violating the social norm in so doing. We also suppose that the extent of disutility falls as more other adults have their children work. We then explore how the total amount of child labor in an economy changes as adults’ labor efficiencies rise or become more unequal. Our analysis reveals that a more equal distribution or rises in adults’ labor efficiency help decrease child labor only under certain conditions.     

Optimal training plans on physical performance considering supercompensation

Abstract

A quantitative evaluation of athletic training is one of the most important issues in the sports science, and its optimization problem between fitness and fatigue has to be considered. Although fitness is the gain of athletic training and athletes can acquire extensive fitness by hard training, they cannot continue such training for a long time because of fatigue. After the hard training which exceeds the physical capacity of athletes, a delayed onset muscle soreness (DOMS) appears and they cannot continue the same training hereafter. Because DOMS impedes the progress of training, it must be avoided when the training plan is made. By continuing training for a long period, the performance capacity of athlete body has enhanced and they can endure hard and long training with which it could not tolerate before, and such performance capacity enhancement is called supercompensation. In a planning athletic training, its optimization problem between fitness and fatigue should be discussed considering, both DOMS and supercompensation by forming probabilistic models of fitness and fatigue, optimal training plans which maximize the total fitness during training periods and minimize the occurrence of DOMS are discussed analytically and numerically.     

Restricted mean survival time as a summary measure of time‐to‐event outcome

Many clinical research studies evaluate a time‐to‐event outcome, illustrate survival functions, and conventionally report estimated hazard ratios to express the magnitude of the treatment effect when comparing between groups. However, it may not be straightforward to interpret the hazard ratio clinically and statistically when the proportional hazards assumption is invalid. In some recent papers published in clinical journals, the use of restricted mean survival time (RMST) or τ ‐year mean survival time is discussed as one of the alternative summary measures for the time‐to‐event outcome. The RMST is defined as the expected value of time to event limited to a specific time point corresponding to the area under the survival curve up to the specific time point. This article summarizes the necessary information to conduct statistical analysis using the RMST, including the definition and statistical properties of the RMST, adjusted analysis methods, sample size calculation, information fraction for the RMST difference, and clinical and statistical meaning and interpretation. Additionally, we discuss how to set the specific time point to define the RMST from two main points of view. We also provide developed SAS codes to determine the sample size required to detect an expected RMST difference with appropriate power and reconstruct individual survival data to estimate an RMST reference value from a reported survival curve.     

Replacement policies for age and working numbers with random life cycle

It has been modeled for several replacement policies in literatures that the whole life cycle or operating interval of an operating unit should be finite rather than infinite as is done with the traditional method. However, it is more natural to consider the case in which the finite life cycle is a fluctuated parameter that could be used to estimate replacement times, which will be taken up in this article. For this, we first formulate a general model in which the unit is replaced at random age U, random time Y for the first working number, random life cycle S, or at failure X, whichever occurs first. The following models included in the general model, such that replacement done at age T when variable U is a degenerate distribution, and replacement done at working numbers N summed by number N of variable Y, are optimized. We obtain the total expected cost until replacement and the expected replacement cost rate for each model. Optimal age T, working number N, and a pair of (T, N) are discussed analytically and computed numerically.