The star-shaped Λ-coalescent and Fleming–Viot process

The star-shaped Λ-coalescent and corresponding Λ-Fleming–Viot process, where the Λ measure has a single atom at unity, are studied in this article. The transition functions and stationary distribution of the Λ-Fleming–Viot process are derived in a two-type model with mutation. The distribution of the number of non-mutant lines back in time in the star-shaped Λ-coalescent is found. Extensions are made to a model with d types, either with parent-independent mutation or general Markov mutation, and an infinitely-many-types model, when d → ∞. An eigenfunction expansion for the transition functions is found, which has polynomial right eigenfunctions and left eigenfunctions described by hyperfunctions. A further star-shaped model with general frequency-dependent change is considered and the stationary distribution in the Fleming–Viot process derived. This model includes a star-shaped Λ-Fleming–Viot process with mutation and selection. In a general Λ-coalescent explicit formulae for the transition functions and stationary distribution, when there is mutation, are unknown. However, in this article, explicit formulae are derived in the star-shaped coalescent.     

Identifiable finite mixtures of location models for clustering mixed-mode data

For clustering mixed categorical and continuous data, Lawrence and Krzanowski (1996) proposed a finite mixture model in which component densities conform to the location model. In the graphical models literature the location model is known as the homogeneous Conditional Gaussian model. In this paper it is shown that their model is not identifiable without imposing additional restrictions. Specifically, for g groups and m locations, (g!)m–1 distinct sets of parameter values (not including permutations of the group mixing parameters) produce the same likelihood function. Excessive shrinkage of parameter estimates in a simulation experiment reported by Lawrence and Krzanowski (1996) is shown to be an artifact of the model's non-identifiability. Identifiable finite mixture models can be obtained by imposing restrictions on the conditional means of the continuous variables. These new identified models are assessed in simulation experiments. The conditional mean structure of the continuous variables in the restricted location mixture models is similar to that in the underlying variable mixture models proposed by Everitt (1988), but the restricted location mixture models are more computationally tractable.     

On perfect simulation for some mixtures of distributions

This paper studies the implementation of the coupling from the past (CFTP) method of Propp and Wilson (1996) in the set-up of two and three component mixtures with known components and unknown weights. We show that monotonicity structures can be exhibited in both cases, but that CFTP can still be costly for three component mixtures. We conclude with a simulation experiment exhibiting an almost perfect sampling scheme where we only consider a subset of the exhaustive set of starting values.     

Seat belt laws: why we should keep them

In the June 2007 issue of Significance , John Adams argued for the repeal of seat belt laws. They have never been demonstrated to save lives, he said; and they increase the number of pedestrians and cyclists killed on the roads. Richard Allsop, Oliver Carsten, Andrew Evans and Robert Gifford argue that Parliament should keep the seat belt laws on the statute book and that we should all keep wearing belts whenever we travel in a car, van or coach—and they contest John's statistics.     

Inference for quantile measures of kurtosis,peakedness, and tail weight

Insight into measures of peakedness, heavy-tailedness, and kurtosis can be gained by studying Ruppert’s ratios of interquantile ranges. They are not only monotone in Horn’s measure of peakedness when applied to the central portion of the population, but also monotone in the practical tail-index of Morgenthaler and Tukey, when applied to the tails. Non-parametric confidence intervals are found for Ruppert’s ratios, and sample sizes required to obtain such intervals for a pre-specified relative width and level are provided. In addition, the empirical power of distribution-free tests for peakedness and bimodality are found for some symmetric distributions.     

The utilitarian contract: A generalization of Rawls' theory of justice

In a series of major papers culminating in A Theory of Justice, John Rawls constructs an alternative to utilitarianism by developing a social contract theory of moral and political philosophy. Unfortunately, Rawls formulates the two basic principles upon which the theory rests in such a way as to restrict (unduly) the contract theory's applicability (see Section I). In this paper we present a more general discussion of the theory of justice that avoids the problems of Rawls' formulation and yet retains the important idea of justice as fairness and the contractarian approach (Section II). Later it is argued that this more general theory constitutes a bridge between the pure utilitarian theories and the social contract doctrines (Sections V and VI). The theory's advantages are demonstrated by applying it to a problem discussed by Rawls, intergenerational equity, and comparing the two solutions (Section III). Further comparisons are made and inferences drawn in the concluding three sections.Without implicating them, we would like to thank James M. Buchanan and David Lyons for comments on an earlier draft of this paper.

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Speaking Truth to Power and Power to Truth: Reflections from the Pandemic

Public Organization Review - The complex relationship between science and politics has been a perennial issue in public administration. In this debate it is important to distinguish between...     

Debiasing or regularisation? Two interpretations of the concept of ‘true preference’ in behavioural economics

Theory and Decision - I reconsider Bleichrodt, Pinto Prades and Wakker’s (BPW) 2001 paper about eliciting utility measures from stated preference surveys. That paper pioneers a method that is...     

Supporting the agency of cities as climate migration destinations

As climate migration has garnered the interest of research and policy communities over the last two decades, the focus has been on whether, how and where climate stresses might precipitate out-migration, and how to assist and protect those affected. Less attention has gone to the places that receive climate migrants, and how their arrival might affect adaptation at destination. Against the backdrop of increasingly severe climate disruptions, this paper examines the likelihood of climate-related movements going into urban areas, and the challenges that this may entail for those who move and for urban governance. With much of climate migration projected to feed into existing urbanization trends, we see the need for data and research to help bolster the agency of communities and cities to plan and act locally, and across geographies, for inclusion and resilience, and to advocate collectively for enabling policy frameworks and increased national and international support.