Allometric Scaling: Analysis of LD50 Data

The need to identify toxicologically equivalent doses across different species is a major issue in toxicology and risk assessment. In this article, we investigate interspecies scaling based on the allometric equation applied to the single, oral LD ₅₀ data previously analyzed by Rhomberg and Wolff.⁽ 1 ⁾ We focus on the statistical approach, namely, regression analysis of the mentioned data. In contrast to Rhomberg and Wolff's analysis of species pairs, we perform an overall analysis based on the whole data set. From our study it follows that if one assumes one single scaling rule for all species and substances in the data set, then β= 1 is the most natural choice among a set of candidates known in the literature. In fact, we obtain quite narrow confidence intervals for this parameter. However, the estimate of the variance in the model is relatively high, resulting in rather wide prediction intervals.     

Consistency of maximum likelihood estimators in a large class of deconvolution models

We consider the maximum likelihood estimator $\hat{F}_n$ of a distribution function in a class of deconvolution models where the known density of the noise variable is of bounded variation. This class of noise densities contains in particular bounded, decreasing densities. The estimator $\hat{F}_n$ is defined, characterized in terms of Fenchel optimality conditions and computed. Under appropriate conditions, various consistency results for $\hat{F}_n$ are derived, including uniform strong consistency. The Canadian Journal of Statistics 41: 98–110; 2013 © 2012 Statistical Society of Canada     

Difficulties in Shifting from Individualistic to Socio-political Policy Regarding Disability in Canada

An individualistic conception of disability has been replaced by a socio-political definition. The socio-political model implies that disability stems from the failure of the social environment to adjust to the needs of people with disabilities rather than from the inability of disabled individuals to adapt to societal demands. This paper will examine the extent to which Canadian policies have changed to embrace this new definition. There has been some progress in policies related to shelter, transportation and recreation. However, policies related to income and employment are still individualistic in nature because policy change in these areas requires a major shift in governmental approach to unemployment and fundamental reform of the Social Assistance system. In a period of high unemployment, people with disabilities are viewed as surplus labour, and the Canadian government has found that high unemployment is politically tolerable. Obstacles to an increase in income support include a strong work ethic, the philosophy that social assistance benefits should be less than could be earned in the work-force, and the private insurance and litigation industries which benefit from the current income system. Other barriers to change are the lack of power of disabled groups and the dominance of professionals.     

Employment after spinal cord injury: the impact of government policies in Canada

The British Columbia Paraplegic Association (BCPA) sought a research partnership to evaluate where its activities should be focused. A survey of members with disabilities of the BCPA included questions on employment and identified three priorities related to employment. These were the need for assistance in finding appropriate work, the impact of policies of government and insurance agencies, and attitudes of employers. This paper examines the social and political environment related to employment following spinal cord injury in British Columbia, Canada. There is no coherent set of goals underlying government employment and income programs in Canada. Incremental development of particular employment and income programs during the 20th century led to a patchwork of policies and programs, which deal with people differently according to the cause of their disability. Federal and provincial governments have attempted to educate employers and reduce barriers to employment of those with disabilities by focusing on anti-discrimination legislation and individual rights (e.g. the Employment Equity Act and the Canadian Human Rights Act). However, people with disabilities face non-accommodating environments, inadequate income support, lack of opportunities and little political influence which stem from an unfair distribution of societal resources, not from discrimination. Joint efforts of the BCPA and other disability organizations are likely to have the most impact on legislative changes.     

Isotonic L2-projection test for local monotonicity of a hazard

We introduce a test statistic for testing the null hypothesis that the sampling distribution has a strictly increasing hazard rate on a specified interval [a,b]$[a,b]$. It is based on a comparison of the empirical distribution function with a shape-constrained estimate, using the restriction that the hazard is increasing. Its asymptotic (normal) distribution was recently derived in Groeneboom and Jongbloed (submitted for publication). We discuss a bootstrap method for computing the critical values and compare the test, thus obtained, with other recently proposed methods in a simulation study. Moreover, we prove that the bootstrap method works asymptotically. In proving that the (smooth and isotonic) bootstrap method works, we derive some results that seem to be of independent interest.     

On the identifiability of copulas in bivariate competing risks models

In competing risks models, the joint distribution of the event times is not identifiable even when the margins are fully known, which has been referred to as the “identifiability crisis in competing risks analysis” (Crowder, 1991). We model the dependence between the event times by an unknown copula and show that identification is actually possible within many frequently used families of copulas. The result is then extended to the case where one margin is unknown. The Canadian Journal of Statistics 41: 291–303; 2013 © 2013 Statistical Society of Canada     

Sieved Maximum Likelihood Estimation in Wicksell's Problem and Related Deconvolution Problems

It is shown that the classical Wicksell problem is related to a deconvolution problem where the convolution kernel is unbounded, convex and decreasing on (0, ∞). For that type of deconvolution problems, the usual non-parametric maximum likelihood estimator of the distribution function is shown not to exist. A sieved maximum likelihood estimator is defined, and some algorithms are described that can be used to compute this estimator. Moreover, this estimator is proved to be strongly consistent.     

Threshold selection for regional peaks-over-threshold data

A hurdle in the peaks-over-threshold approach for analyzing extreme values is the selection of the threshold. A method is developed to reduce this obstacle in the presence of multiple, similar data samples. This is for instance the case in many environmental applications. The idea is to combine threshold selection methods into a regional method. Regionalized versions of the threshold stability and the mean excess plot are presented as graphical tools for threshold selection. Moreover, quantitative approaches based on the bootstrap distribution of the spatially averaged Kolmogorov–Smirnov and Anderson–Darling test statistics are introduced. It is demonstrated that the proposed regional method leads to an increased sensitivity for too low thresholds, compared to methods that do not take into account the regional information. The approach can be used for a wide range of univariate threshold selection methods. We test the methods using simulated data and present an application to rainfall data from the Dutch water board Vallei en Veluwe.