Life, Death and Preferential Attachment

Scientific communities are characterized by strong stratification. The highly skewed frequency distribution of citations of published scientific papers suggests a relatively small number of active, cited papers embedded in a sea of inactive and uncited papers. We propose an analytically soluble model which allows for the death of nodes. This model provides an excellent description of the citation distributions for live and dead papers in the SPIRES database. Further, this model suggests a novel and general mechanism for the generation of power law distributions in networks whenever the fraction of active nodes is small.Comment: 5 pages, 2 figure

Belief in conspiracy theories and intentions to engage in everyday crime

Belief in conspiracy theories is associated with negative outcomes such as political disengagement, prejudice, and environmental inaction. The current studies - one cross-sectional (N = 253) and one experimental (N = 120) - tested the hypothesis that belief in conspiracy theories would increase intentions to engage in everyday crime. Study 1 demonstrated that belief in conspiracy theories predicted everyday crime behaviours when controlling for other known predictors of everyday crime (e.g., Honesty-Humility). Study 2 demonstrated that exposure to conspiracy theories (vs. control) increased intentions to engage in everyday crime in the future, through an increased feeling of anomie. The perception that others have conspired may therefore in some contexts lead to negative action rather than inaction

Generalized pricing formulas for stochastic volatility jump diffusion models applied to the exponential Vasicek model

Path integral techniques for the pricing of financial options are mostly based on models that can be recast in terms of a Fokker-Planck differential equation and that, consequently, neglect jumps and only describe drift and diffusion. We present a method to adapt formulas for both the path-integral propagators and the option prices themselves, so that jump processes are taken into account in conjunction with the usual drift and diffusion terms. In particular, we focus on stochastic volatility models, such as the exponential Vasicek model, and extend the pricing formulas and propagator of this model to incorporate jump diffusion with a given jump size distribution. This model is of importance to include non-Gaussian fluctuations beyond the Black-Scholes model, and moreover yields a lognormal distribution of the volatilities, in agreement with results from superstatistical analysis. The results obtained in the present formalism are checked with Monte Carlo simulations.Comment: 9 pages, 2 figures, 1 tabl

Stochastic Cellular Automata Model for Stock Market Dynamics

In the present work we introduce a stochastic cellular automata model in order to simulate the dynamics of the stock market. A direct percolation method is used to create a hierarchy of clusters of active traders on a two dimensional grid. Active traders are characterised by the decision to buy, (+1), or sell, (-1), a stock at a certain discrete time step. The remaining cells are inactive,(0). The trading dynamics is then determined by the stochastic interaction between traders belonging to the same cluster. Most of the stylized aspects of the financial market time series are reproduced by the model.Comment: 17 pages and 7 figure

Engineering serendipity: When does knowledge sharing lead to knowledge production?

Research Summary We investigate how knowledge similarity between two individuals is systematically related to the likelihood that a serendipitous encounter results in knowledge production. We conduct a field experiment at a medical research symposium, where we exogenously varied opportunities for face‐to‐face encounters among 15,817 scientist‐pairs. Our data include direct observations of interaction patterns collected using sociometric badges, and detailed, longitudinal data of the scientists\u27 postsymposium publication records over 6 years. We find that interacting scientists acquire more knowledge and coauthor 1.2 more papers when they share some overlapping interests, but cite each other\u27s work between three and seven times less when they are from the same field. Our findings reveal both collaborative and competitive effects of knowledge similarity on knowledge production outcomes. Managerial Summary Managers often try to stimulate innovation by encouraging serendipitous interactions between employees, for example by using office space redesigns, conferences and similar events. Are such interventions effective? This article proposes that an effective encounter depends on the degree of common knowledge shared by the individuals. We find that scientists who attend the same conference are more likely to learn from each other and collaborate effectively when they have some common interests, but may view each other competitively when they work in the same field. Hence, when designing opportunities for face‐to‐face interactions, managers should consider knowledge similarity as a criteria for fostering more productive exchanges

A Delayed Black and Scholes Formula I

In this article we develop an explicit formula for pricing European options when the underlying stock price follows a non-linear stochastic differential delay equation (sdde). We believe that the proposed model is sufficiently flexible to fit real market data, and is yet simple enough to allow for a closed-form representation of the option price. Furthermore, the model maintains the no-arbitrage property and the completeness of the market. The derivation of the option-pricing formula is based on an equivalent martingale measure

What role for public policy in promoting philanthropy? The case of EU universities

This article presents and discusses the findings of a survey conducted among Higher Educational Institutions (HEIs) in most of the twenty-seven countries within the European Union, which studied the extent and success of fundraising from philanthropic sources for research. Our data demonstrate that success in fundraising is related to institutional privilege (in terms of the universities' reputation, wealth and networks) as well as factors relating to the internal organization, activities and cultures of universities (such as the extent of investment in fundraising activities) and factors relating to the external social, economic and political environments (such as national cultural attitudes towards philanthropy and the existence of tax breaks for charitable giving). Our findings identify the existence of a ‘Matthew effect’, such that privilege begets privilege, when it comes to successful fundraising for university research. We argue that, despite the existence of some untapped philanthropic potential, not all universities are equally endowed with the same fundraising capacities. The article concludes by suggesting that policy-makers pay more heed to the structural constraints within which fundraising takes place, to ensure that policies that seek to promote philanthropy are realistic

The Effect of Bankruptcy Laws on the Valuation of Risky Consumer Debt

In a market setting with perfect information, a consumer recognizes that he can influence the state-contingent returns, and hence the pric, of his risky debt by the decision variables that determine the collateral and promised payments. This paper examines the effect of bankruptcy laws on the feasible consumption opportunities of borrowers and lenders in order to determine the necessary requirements for the bilateral debt market to be perfectly competitive.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72017/1/j.1540-6288.1989.tb00348.x.pd

Escaping from Poverty: Household Income Dynamics in Indonesia, South Africa, Spain, and Venezuela

[Excerpt] This study presents the main results of a larger, more technical report (Fields and others 2001) and subsequent work (Fields and others 2002) that analyzes income mobility in Indonesia, South Africa, Spain, and Venezuela. These economies were selected on the basis of the availability of panel data with which to analyze household income dynamics in the 1990s. By following households over time, we are able to investigate how households that were poor initially fared economically, relative to their richer counterparts. We can learn more about how and why households exit—and enter—poverty. To gauge income mobility, this study centers on the change in household per capita income over time, using two measures. Our first measure—a conventional one—gauges income changes in currency units. Our second measure, the change in log currency units, approximates the percentage changes in income. In this way, it arguably better reflects the reality of a poor household, in which a given change in income—whether an increase or a decrease—counts more than it does in a richer one.Fields9_Escaping_From_Poverty.pdf: 544 downloads, before Oct. 1, 2020

Parental ethnic identity and child test scores

We examine the relationship between parental ethnic identity and the test scores of ethnic minority children. We use standard survey measures of the strength of parental identity alongside validated cognitive test scores in a rich British cohort study. We show that children whose mothers report either an adoption or an active rejection of the majority identity tend to score lower in cognitive tests at age 7, compared to those children whose mothers report neutral feelings about the majority identity. We find no consistent differences in test scores according to mothers’ minority identity. Our findings provide no support for education or citizenship policies which promote the adoption of the majority identity or discourage the maintenance of separate identities in ethnic minority communities