A note on the non-negativity of continuous-time ARMA and GARCH processes

A general approach for modeling the volatility process in continuous-time is based on the convolution of a kernel with a non-decreasing Lévy process, which is non-negative if the kernel is non-negative. Within the framework of Continuous-time Auto-Regressive Moving-Average (CARMA) processes, we derive a necessary condition for the kernel to be non-negative, and propose a numerical method for checking the non-negativity of a kernel function. These results can be lifted to solving a similar problem with another approach to modeling volatility via the COntinuous-time Generalized Auto-Regressive Conditional Heteroscedastic (COGARCH) processes.     

Mixture of latent trait analyzers for model-based clustering of categorical data

Model-based clustering methods for continuous data are well established and commonly used in a wide range of applications. However, model-based clustering methods for categorical data are less standard. Latent class analysis is a commonly used method for model-based clustering of binary data and/or categorical data, but due to an assumed local independence structure there may not be a correspondence between the estimated latent classes and groups in the population of interest. The mixture of latent trait analyzers model extends latent class analysis by assuming a model for the categorical response variables that depends on both a categorical latent class and a continuous latent trait variable; the discrete latent class accommodates group structure and the continuous latent trait accommodates dependence within these groups. Fitting the mixture of latent trait analyzers model is potentially difficult because the likelihood function involves an integral that cannot be evaluated analytically. We develop a variational approach for fitting the mixture of latent trait models and this provides an efficient model fitting strategy. The mixture of latent trait analyzers model is demonstrated on the analysis of data from the National Long Term Care Survey (NLTCS) and voting in the U.S. Congress. The model is shown to yield intuitive clustering results and it gives a much better fit than either latent class analysis or latent trait analysis alone.     

Governing police practice: limits of the new accountability

The advent of public-sector managerialism has brought with it a new principle of police accountability in Western democracies such as Australia and Britain. The new accountability gives emphasis to managerial rather than legal or public-interest standards, favours external oversight combined with self-regulation rather than centralized control, and promotes risk management rather than rule enforcement. This article makes use of the experience of an Australian police force to show that the new accountability has not been successful in holding police accountable, while elements of the old accountability have re-emerged to dominate public debates. It is argued that in the area of police governance, the neo-liberal state does not necessarily pursue a coherent strategy of 'acting at a distance' (cf. Miller and Rose 1990), partly because of the inability of accountability technologies to deliver substantially the promised policy outcomes and partly because of the sensitivity of its political arm to the public's moral outrage against corruption (cf. Garland 1996).     

A New Model of Trend Inflation

This article introduces a new model of trend inflation. In contrast to many earlier approaches, which allow for trend inflation to evolve according to a random walk, ours is a bounded model which ensures that trend inflation is constrained to lie in an interval. The bounds of this interval can either be fixed or estimated from the data. Our model also allows for a time-varying degree of persistence in the transitory component of inflation. In an empirical exercise with CPI inflation, we find the model to work well, yielding more sensible measures of trend inflation and forecasting better than popular alternatives such as the unobserved components stochastic volatility model. This article has supplementary materials online.     

Defining Nations in Asia and Europe: A Comparative Analysis of Ethnic Return Migration Policy1

We argue that regional comparison of East Asian and European ethnic return migration policy offers important new perspectives on nationhood, nondiscrimination norms, and trans‐nationality. We find that despite international nondiscrimination norms, preferential ethnic return policy is common in both regions. These policies at least implicitly define the nation as existing across borders. However, there are significant regional differences. East Asian states use co‐ethnic preferences instrumentally for economic goals and also offer preferential treatment of co‐ethnic foreign investors. European states offer preferences to coethnics to protect these populations or express symbolic ties, sometimes at great expense. Thus, in Europe the state has an obligation to assist coethnics abroad, but in Asia, foreign coethnics assist the state.     

中国城市群基本概念的再认知

城市群并不是孤立封闭的体系,它是与邻近区域内、特别是经济发达的城镇密集区的特定区域范围内不同规模的城市(镇)有着密切联系,依托优越的自然环境基础和发达的交通运输体系以及信息网络形成的一个比较完整的有机整体。尤其是在全球经济一体化以及新型城镇化的新形势下,城市群区内每一个城市均发挥着区域经济增长点和城市功能的特殊作用,并依托城乡一体化区域发挥着强大的辐射作用(包括集聚与疏散作用)。本文在这一基础上深入分析了中国城市群是由城镇化高度发育而形成这一动力问题;论证城市群与城镇密集区的相似性,并对我国城市群范围的识别标准和城市群基本概念的再认识,比较完整地概括了当前我国城市群研究动态与阶段性成果,以供我国城市地理与经济学工作者参考,以便更加深入地研究中国城市群的特有现象和各类问题。     

Contested news values and media performance during the Umbrella Movement

Social crises are a huge challenge to the performance of the media. The norms and routines of news making with which journalists comply can become problematic in the context of intensive public sentiment and empathy. News values, including the sacred belief in objective reporting, are questioned in the light of controversies over editorial judgment within and outside the newsroom. I examine the contested news values that manifested in the Umbrella Movement of Hong Kong in 2014. In particular, I focus on the arguments and deliberations regarding news objectivity, which involved several parameters of the performance of the media during this social crisis.