Statistical physics of human cooperation

Extensive cooperation among unrelated individuals is unique to humans, who often sacrifice personal benefits for the common good and work together to achieve what they are unable to execute alone. The evolutionary success of our species is indeed due, to a large degree, to our unparalleled other-regarding abilities. Yet, a comprehensive understanding of human cooperation remains a formidable challenge. Recent research in social science indicates that it is important to focus on the collective behavior that emerges as the result of the interactions among individuals, groups, and even societies. Non-equilibrium statistical physics, in particular Monte Carlo methods and the theory of collective behavior of interacting particles near phase transition points, has proven to be very valuable for understanding counterintuitive evolutionary outcomes. By studying models of human cooperation as classical spin models, a physicist can draw on familiar settings from statistical physics. However, unlike pairwise interactions among particles that typically govern solid-state physics systems, interactions among humans often involve group interactions, and they also involve a larger number of possible states even for the most simplified description of reality. The complexity of solutions therefore often surpasses that observed in physical systems. Here we review experimental and theoretical research that advances our understanding of human cooperation, focusing on spatial pattern formation, on the spatiotemporal dynamics of observed solutions, and on self-organization that may either promote or hinder socially favorable states.

Mobility can bring opportunities for coping with environmental change, say Richard Black, Stephen R. G. Bennett, Sandy M. Thomas and John R. Beddington.

/pdf/climate-change-migration-as-adaptation-3n820ibivg.pdf

Climate change: Migration as adaptation

Functions of One Complex Variable

This review is intended to provide a critical and up-to-date survey of the analytical approximate methods that are encountered in scattering from random rough surfaces. The underlying principles of the different methods are evidenced and the functional form of the corresponding scattering amplitude or cross-section is given. The reader is referred to the original papers in order to obtain the explicit expressions of the coefficients and kernels. We have tried to identify the main strengths and weaknesses of the various theories. We provide synthetic tables of their respective performances, according to a dozen important requirements a valuable method should meet. Both scalar acoustic and vector electromagnetic theories are equally addressed.

/pdf/a-critical-survey-of-approximate-scattering-wave-theories-247gglp03m.pdf

A critical survey of approximate scattering wave theories from random rough surfaces

Using newly available census data, the stock of international migrants is estimated at 247 million in 2013, significantly larger than the previous estimate of 232 million, and is expected to surpass 250 million in 2015. Migrants’ remittances to developing countries are estimated to have reached $436 billion in 2014, a 4.4 percent increase over the 2013 level. All developing regions recorded positive growth except Europe and Central Asia (ECA), where remittance flows contracted due to the deterioration of the Russian economy and the depreciation of the ruble. In 2015, however, the growth of remittance flows to developing countries is expected to moderate sharply to 0.9 percent to $440 billion, led by a 12.7 percent decline in ECA and slowdown in East Asia and the Pacific, Middle-East and North Africa, and Sub-Saharan Africa. The positive impact on flows of a robust recovery in the US will be partially offset by continued weakness in Europe, the impact of lower oil prices on the Russian economy, the strengthening of the US dollar, and tighter immigration controls in many source countries for remittances. Remittance flows are expected to recover in 2016 to reach $479 billion by 2017, in line with the more positive global economic outlook.

/pdf/migration-and-remittances-recent-developments-and-outlook-2rmky6n5za.pdf

Migration and remittances : recent developments and outlook

Motivated by the need for parametric families of rich and yet tractable distributions in financial mathematics, both in pricing and risk management settings, but also considering wider statistical applications, we investigate a novel technique for introducing skewness or kurtosis into a symmetric or other distribution. We use a "transmutation" map, which is the functional composition of the cumulative distribution function of one distribution with the inverse cumulative distribution (quantile) function of another. In contrast to the Gram-Charlier approach, this is done without resorting to an asymptotic expansion, and so avoids the pathologies that are often associated with it. Examples of parametric distributions that we can generate in this way include the skew-uniform, skew-exponential, skew-normal, and skew-kurtotic-normal.

The alchemy of probability distributions: beyond Gram-Charlier expansions, and a skew-kurtotic-normal distribution from a rank transmutation map

International migration has profound implications for human welfare, and African governments have had only a limited influence on welfare outcomes, for good or ill. Improved efforts to manage migration will require information on the nature and impact of migratory patterns. This book seeks to contribute toward this goal, by reviewing previous research and providing new analyses (including surveys and case studies) as well as by formulating policy recommendations that can improve the migration experience for migrants, origin countries, and destination countries. The book comprises this introduction and summary and four chapters. Chapter one reviews the data on African migration and considers the challenges African governments face in managing migration. Chapter two discusses the importance of remittances, the most tangible link between migration and development; it also identifies policies that can facilitate remittance flows to Africa and increase their development impact. Chapter three analyzes high-skilled emigration and analyzes policies that can limit adverse implications and maximize positive implications for development. Chapter four considers ways in which Africa can leverage its diaspora resources to increase trade, investment, and access to technology.

/pdf/leveraging-migration-for-africa-remittances-skills-and-qxplb1mgj1.pdf

Leveraging Migration for Africa: Remittances, Skills, and Investments

The statistical signatures of the 'credit crunch' financial crisis that unfolded between 2008 and 2009 are investigated by combining tools from statistical physics and network theory. We devise measures for the collective behavior of stock prices based on the construction of topologically constrained graphs from cross-correlation matrices. We test the stability, statistical significance and economic meaningfulness of these graphs. The results show an intriguing trend that highlights a consistently decreasing centrality of the financial sector over the last 10 years.

/pdf/correlation-structure-and-dynamics-in-volatile-markets-4j7wx9xdm8.pdf

Correlation structure and dynamics in volatile markets

This book takes a fresh look at export diversification. It concludes that much of the recent literature, though novel, has focused excessively on simply adding new products to export portfolios. One branch of these studies centers on the 'discovery' of exports, and it argues that the threat of entry (imitation) leads to an underinvestment in bringing new products to the global market. Another analytical branch focuses on changing the contents of an export portfolio to mirror the exports of countries with higher incomes on the grounds that these lead to higher productivity. Both strands implicitly point to the need for careful yet active government policies. While such policies are important, this book argues for a more comprehensive view of diversification and hence a more comprehensive trade policy strategy-one that takes into account improving the quality of existing exports, breaking into new geographic markets, and increasing services exports. This publication has been tailored to policy makers, their staffs, and the international development community at large. It is a collection of short articles that summarize major issues and policies on particular topics. Many of the chapters are digests of more formal studies but are presented here with a minimum of underlying econometric and theoretical detail of less interest to policy makers. As the World Bank increases its efforts on 'aid for trade,' Staff are working with countries to help diversify their exports. Along with other development partners, the Bank is providing enhanced assistance to improve competitiveness, facilitate trade, improve trade-related services, and exploit regional and multilateral initiatives to open markets for developing countries. This book makes a substantial contribution to the efforts of developing countries to use the global economy to spur growth and reduce poverty.

William T. Shaw

Papers

Migration and remittances : recent developments and outlook

The alchemy of probability distributions: beyond Gram-Charlier expansions, and a skew-kurtotic-normal distribution from a rank transmutation map

Leveraging Migration for Africa: Remittances, Skills, and Investments

Correlation structure and dynamics in volatile markets

Breaking Into New Markets