Using parallel computation to improve Independent Metropolis--Hastings based estimation

In this paper, we consider the implications of the fact that parallel raw-power can be exploited by a generic Metropolis--Hastings algorithm if the proposed values are independent. In particular, we present improvements to the independent Metropolis--Hastings algorithm that significantly decrease the variance of any estimator derived from the MCMC output, for a null computing cost since those improvements are based on a fixed number of target density evaluations. Furthermore, the techniques developed in this paper do not jeopardize the Markovian convergence properties of the algorithm, since they are based on the Rao--Blackwell principles of Gelfand and Smith (1990), already exploited in Casella and Robert (1996), Atchade and Perron (2005) and Douc and Robert (2010). We illustrate those improvements both on a toy normal example and on a classical probit regression model, but stress the fact that they are applicable in any case where the independent Metropolis-Hastings is applicable.Comment: 19 pages, 8 figures, to appear in Journal of Computational and Graphical Statistic

Stuck in Traffic: The Effects of Regional Trade on Human Trafficking

Human trafficking represents one negative side affect of an increasingly interconnected, globalized world. What characteristics of regional trade drive bilateral human trafficking flows? Resource dependent states, or states with an economy established primarily through resource exports, interact with more industrialized states to push and pull populations into human trafficking schemes as a byproduct of economic and political linkages. The adverse conditions of resource dependence push populations into trafficking networks while traffickers and trafficking victims are drawn to economic opportunity in more stable regional trade partners. This theory is tested using ordinal logistic and OLS regression, utilizing cross sectional and time series datasets that capture both trafficking flows and state efforts to combat trafficking. The analyses support the theoretical expectation that economic linkage between resource dependent states and industrial states is positively associated with human trafficking rates for both destination and source countries. In conclusion, different causal factors for human trafficking may be at work in source and destination states

Diffusion of Lexical Change in Social Media

Computer-mediated communication is driving fundamental changes in the nature of written language. We investigate these changes by statistical analysis of a dataset comprising 107 million Twitter messages (authored by 2.7 million unique user accounts). Using a latent vector autoregressive model to aggregate across thousands of words, we identify high-level patterns in diffusion of linguistic change over the United States. Our model is robust to unpredictable changes in Twitter's sampling rate, and provides a probabilistic characterization of the relationship of macro-scale linguistic influence to a set of demographic and geographic predictors. The results of this analysis offer support for prior arguments that focus on geographical proximity and population size. However, demographic similarity -- especially with regard to race -- plays an even more central role, as cities with similar racial demographics are far more likely to share linguistic influence. Rather than moving towards a single unified "netspeak" dialect, language evolution in computer-mediated communication reproduces existing fault lines in spoken American English.Comment: preprint of PLOS-ONE paper from November 2014; PLoS ONE 9(11) e11311

How an elevator can be key to a candidate’s electoral success

Can candidates use non-campaign advertising to help them to win elections? Using the example of North Carolina Commissioner of Labor Cherie Berry – who has her picture placed in every elevator in the state – Jacob Smith and Neil Weinberg find that this non-campaign advertising did increase her share of the vote. They write that in an era when races in competitive states like North Carolina are decided by only few percentage points, such an effect has the potential to swing the outcome of elections

Experimental Performance of a Quantum Simulator: Optimizing Adiabatic Evolution and Identifying Many-Body Ground States

We use local adiabatic evolution to experimentally create and determine the ground state spin ordering of a fully-connected Ising model with up to 14 spins. Local adiabatic evolution -- in which the system evolution rate is a function of the instantaneous energy gap -- is found to maximize the ground state probability compared with other adiabatic methods while only requiring knowledge of the lowest $\sim N$ of the $2^N$ Hamiltonian eigenvalues. We also demonstrate that the ground state ordering can be experimentally identified as the most probable of all possible spin configurations, even when the evolution is highly non-adiabatic