Modeling the Rise in Internet-based Petitions

Contemporary collective action, much of which involves social media and other Internet-based platforms, leaves a digital imprint which may be harvested to better understand the dynamics of mobilization. Petition signing is an example of collective action which has gained in popularity with rising use of social media and provides such data for the whole population of petition signatories for a given platform. This paper tracks the growth curves of all 20,000 petitions to the UK government over 18 months, analyzing the rate of growth and outreach mechanism. Previous research has suggested the importance of the first day to the ultimate success of a petition, but has not examined early growth within that day, made possible here through hourly resolution in the data. The analysis shows that the vast majority of petitions do not achieve any measure of success; over 99 percent fail to get the 10,000 signatures required for an official response and only 0.1 percent attain the 100,000 required for a parliamentary debate. We analyze the data through a multiplicative process model framework to explain the heterogeneous growth of signatures at the population level. We define and measure an average outreach factor for petitions and show that it decays very fast (reducing to 0.1% after 10 hours). After 24 hours, a petition's fate is virtually set. The findings seem to challenge conventional analyses of collective action from economics and political science, where the production function has been assumed to follow an S-shaped curve.Comment: Submitted to EPJ Data Scienc

How Highly Pathogenic Avian Influenza (H5N1) Has Affected World Poultry-Meat Trade

In 2003, outbreaks of the highly pathogenic avian influenza (HPAI) H5N1 virus had a major negative impact on the global poultry industry. Initially, import demand for both uncooked and cooked poultry declined substantially, due to consumers’ fear of contracting avian influenza by eating poultry meat. Consumer fears adversely affected poultry consumption in many countries, leading to lower domestic prices, decreased production, and lower poultry meat exports. These reductions proved to be short-lived, as prices, consumption, production, and exports returned to preoutbreak levels in a relatively short time. As consumers gained confidence that poultry was safe if properly handled and cooked, world demand for cooked poultry increased. The cooked poultry share of total cooked and uncooked global exports nearly doubled from 2004 to 2006. In 2006, the world poultry industry was again under pressure due to HPAI H5N1 outbreaks, this time in Europe. By the end of the year, however, world poultry meat output had reached a new high, although, for some European countries, it was slightly below the 2005 level.highly pathogenic avian influenza, HPAI H5N1, cooked poultry meat, uncooked poultry meat, poultry exports, domestic poultry prices, export poultry prices, poultry consumption, poultry production, International Relations/Trade, Livestock Production/Industries,

DERIVED FEED DEMAND FOR EGYPT'S POULTRY AND EGG SECTOR TO 2010--POLICIES AND IMPLICATIONS

Egypt's derived feed demand for poultry and eggs and its dependency on world feed markets was econometrically projected to 2010. Results reveal a poultry industry as highly dependent on imports, where dependency rate will approach 100 percent for soybeans and 48 percent for yellow corn in 2010.International Relations/Trade,

IMPACT OF SANITARY AND PHYTO-SANITARY AGREEMENTS ON WORLD TRADE OF POULTRY, AND POULTRY PRODUCTS

Replaced with revised version of paper 07/29/04.Food Consumption/Nutrition/Food Safety, International Relations/Trade,

Bayesian Estimation of Mixed Multinomial Logit Models: Advances and Simulation-Based Evaluations

Variational Bayes (VB) methods have emerged as a fast and computationally-efficient alternative to Markov chain Monte Carlo (MCMC) methods for scalable Bayesian estimation of mixed multinomial logit (MMNL) models. It has been established that VB is substantially faster than MCMC at practically no compromises in predictive accuracy. In this paper, we address two critical gaps concerning the usage and understanding of VB for MMNL. First, extant VB methods are limited to utility specifications involving only individual-specific taste parameters. Second, the finite-sample properties of VB estimators and the relative performance of VB, MCMC and maximum simulated likelihood estimation (MSLE) are not known. To address the former, this study extends several VB methods for MMNL to admit utility specifications including both fixed and random utility parameters. To address the latter, we conduct an extensive simulation-based evaluation to benchmark the extended VB methods against MCMC and MSLE in terms of estimation times, parameter recovery and predictive accuracy. The results suggest that all VB variants with the exception of the ones relying on an alternative variational lower bound constructed with the help of the modified Jensen's inequality perform as well as MCMC and MSLE at prediction and parameter recovery. In particular, VB with nonconjugate variational message passing and the delta-method (VB-NCVMP-Delta) is up to 16 times faster than MCMC and MSLE. Thus, VB-NCVMP-Delta can be an attractive alternative to MCMC and MSLE for fast, scalable and accurate estimation of MMNL models

A Non-Singular Universe in String Cosmology

We consider the low-energy effective string action in four dimensions including the leading order-$\alpha'$ terms. An exact homogeneous solution is obtained. It represents a non-singular expanding cosmological model in which the tensor fields tend to vanish as $t\to \infty$. The scale factor $a(t)$ of the very early universe in this model has the time dependence $a(t)^2=a_0^2+t^2$. The violation of the strong energy condition of classical General Relativity to avoid the initial singularity requires that the central charge deficit of the theory be larger than a certain value. The significance of this solution is discussed.Comment: RevTex, 10 pages, a new reference and related information is adde