Downsizing for downtown: limb lengths,toe lengths,and scale counts decrease with urbanization in western fence lizards (Sceloporus occidentalis)

Urban Ecosystems - Urbanization-induced habitat loss and alteration causes significant challenges for the survival of many species. Identifying how species respond to urbanization can yield...     

Permuting incomplete paired data: a novel exact and asymptotic correct randomization test

Various statistical tests have been developed for testing the equality of means in matched pairs with missing values. However, most existing methods are commonly based on certain distributional assumptions such as normality, 0-symmetry or homoscedasticity of the data. The aim of this paper is to develop a statistical test that is robust against deviations from such assumptions and also leads to valid inference in case of heteroscedasticity or skewed distributions. This is achieved by applying a clever randomization approach to handle missing data. The resulting test procedure is not only shown to be asymptotically correct but is also finitely exact if the distribution of the data is invariant with respect to the considered randomization group. Its small sample performance is further studied in an extensive simulation study and compared to existing methods. Finally, an illustrative data example is analysed.     

Authors’ response: on the role of data,statistics and decisions in a pandemic

AStA Advances in Statistical Analysis -     

Homelessness outcome reporting normative framework: systems-level evaluation of progress in ending homelessness

Homelessness is a serious and growing issue. Evaluations of systemic-level changes are needed to determine progress in reducing or ending homelessness. The report card methodology is one means of systems-level assessment. Rather than solely establishing an enumeration, homelessness report cards can capture pertinent information about structural determinants of homelessness. This information can inform the development of evidence-based strategies aimed at ending (rather than managing) homelessness. To aid in the development of homelessness report card creation, a systems-level Homelessness Outcome Reporting Normative Framework (the HORN Framework) was developed. This article provides an overview of the framework and its application.     

Approximate tests for the equality of two cumulative incidence functions of a competing risk

In the context of a competing risks set-up, we discuss different inference procedures for testing equality of two cumulative incidence functions, where the data may be subject to independent right-censoring or left-truncation. To this end, we compare two-sample Kolmogorov–Smirnov- and Cramér–von Mises-type test statistics. Since, in general, their corresponding asymptotic limit distributions depend on unknown quantities, we utilize wild bootstrap resampling as well as approximation techniques to construct adequate test decisions. Here, the latter procedures are motivated from tests for heteroscedastic factorial designs but have not yet been proposed in the survival context. A simulation study shows the performance of all considered tests under various settings and finally a real data example about bloodstream infection during neutropenia is used to illustrate their application.     

Small sample properties of asymptotically equivalent tests for autoregressive conditional heteroskedasticity

Models that allow for autoregressive conditional heteroskedasticity (ARCH) in the error process have recently found widespread application. The purpose of this paper is to evaluate, through Monte Carlo analysis, the small sample properties of an exact Lagrange multiplier test for the presence of ARCH, and to compare the power of this test with that of an asymptotically equivalent TR² version. The comparison involves first-and higher-order variants of these processes. The results indicate substantial power differentials in favor of the exact LM test, by up to 15% for sample sizes smaller than 100.     

Testing equality of correlation coefficients in two populations via permutation methods

The present paper investigates the asymptotic behaviour of a studentized permutation test for testing equality of (Pearson) correlation coefficients in two populations. It is shown that this test is asymptotically of exact level and has the same power for contiguous alternatives as the corresponding asymptotic test. As a by-product we specify the assumptions needed for the validity of the permutation test suggested in Sakaori (2002). A small simulation study compares the finite sample properties of the considered tests.     

Guaranteed Renewability with Group Insurance

This paper investigates a multiple-period level premium insurance policy equilibrium in a model in which loss probabilities increase for a fixed time period for a set of persons buying insurance in a group. We show that a level-premium sequence which induces risk averse persons to become and remain members of the group exists. We also show that the availability of the Medicare program can prevent the emergence of optimal level-premium private group insurance, but that a system of bonuses for remaining in the group can permit optimality to be retained.