Strategies in social network formation

We run a computerised experiment of network formation where all connections are beneficial and only direct links are costly. Players simultaneously submit link proposals; a connection is made only when both players involved agree. We use both simulated and experimentally generated data to test the determinants of individual behaviour in network formation. We find that approximately 40% of the network formation strategies adopted by the experimental subjects can be accounted for as best responses. We test whether subjects follow alternative patterns of behaviour and in particular if they: propose links to those from whom they have received link proposals in the previous round; propose links to those who have the largest number of direct connections. We find that together with best response behaviour, these strategies explain approximately 75% of the observed choices. We estimate individual propensities to adopt each of these strategies, controlling for group effects. Finally we estimate a mixture model to highlight the proportion of each type of decision maker in the population

Behavioural patterns in social networks

In this paper, we focus on the analysis of individual decision making for the formation of social networks, using experimentally generated data. We first analyse the determinants of the individual demand for links under the assumption of agents' static expectations. The results of this exercise subsequently allow us to identify patterns of behaviour that can be subsumed in three strategies of link formation: 1) reciprocator strategy - players propose links to those from whom they have received link proposals in the previous round; 2) myopic best response strategy - players aim to profit from maximisation; 3) opportunistic strategy - players reciprocate link proposals to those who have the largest number of connections. We find that these strategies explain approximately 76% of the observed choices. We finally estimate a mixture model to highlight the proportion of the population who adopt each of these strategies

Assessing Multiple Prior Models of Behaviour under Ambiguity

The recent spate of theoretical models of behaviour under ambiguity can be partitioned into two sets: those involving multiple priors (in which the probabilities of the various events are not known but probabilities can be attached to the various possible values for the probabilities) and those not involving multiple priors. This paper concentrates on the first set and provides an experimental investigation into recently proposed theories. Using an appropriate experimental interface, in which the probabilities on the various possibilities are explicitly stated, we examine the fitted and predictive power of the various theories. We first estimate subject-by-subject, and then we estimateand predict using a mixture model over the contending theories. The individual estimates suggest that 25% of our 149 subjects have behaviour consistent with Expected Utility, 54% with the Smooth Model (of Klibanoff et al, 2005), 12% with Rank Dependent Expected Utility and 9% with the Alpha Model (of Ghirardato et al 2004); these figures are very close to the mixing proportions obtained from the mixture estimates. However, if we classify our subjects through the posterior probabilities (given all the evidence) of each of them being of the various types: using the estimates we get 38%, 19%, 28% and 16% (for EU, Smooth, Rank Dependent and Alpha); while using the predictions 36%, 19%, 33% and 11%. Interestingly the older models (EU and RD) seem to fare relatively better, suggesting that representing ambiguity through multiple priors is perceived by subjects as risk, rather than ambiguityAlpha Model, Ambiguity, Expected Utility, Mixture Models, Rank Dependent Expected Utility, Smooth Model.

Self-assessed health as a key determinant of lifestyles: An application to tobacco consumption in Argentina

The relationship between lifestyle choices and health has been widely studied in the epidemiological and economic literature. In the last years, empirical research was directed towards the use of recursive systems with structural equations for a health production function and reduced form equations for lifestyles. As a result, behaviors toward health are taken to be determined by exogenous socio-economic variables. In this article, we show that health is a key determinant of health habits. When people feel well, they adopt less healthy behaviors. We use maximum simulated likelihood for a multivariate 5 equation probit model. In that model, lifestyles (diet, exercise, alcohol consumption and smoking) are a function of exogenous socioeconomic variables and self-reported health. Self-reported health varies with socio-economic characteristics and depends on health indicators that are the consequence of lifestyles undertaken in the past (i.e., overweight, blood pressure, diabetes and cholesterol levels). Data is that of adults in Argentina´s 2005 Risk Factors National Survey. We find that health partial effects on lifestyle are much larger having accounted for health endogeneity. Accounting for unobservable variables that jointly determine all lifestyles does not change much the magnitude of our results. Our findings are robust to different specifications.lifestyles, health

A reassessment of Argentina´s GHG proposed target

At the time of Argentina´s greenhouse gases emissions reduction voluntary commitment, most of the articles on intensity targets had not been published. The aim of this paper is to (re)discuss briefly the proposal made by Argentina taking into account that literature. To justify the adopted target form and stringency, we compare fixed and dynamic targets in terms of the likelihood of “hot air”, the relationship between allowed emissions and GDP, the link between abatement and GDP, and outcomes´ dispersion. But, the assumptions implicit in the design of the target may change those properties. We show how the BAU scenario taken as reference and the level of emissions reduction affects targets´ design and characteristics. Finally, considering different emissions projections, we perform a comparison between allowed emissions and projected ones during the first half commitment period (2008-2010), concluding that compliance with the commitment depends on the data source used in the calculations.climate change, intensity targets, uncertainty, Argentina

Integration of a generalized H\'enon-Heiles Hamiltonian

The generalized H\'enon-Heiles Hamiltonian $H=1/2(P_X^2+P_Y^2+c_1X^2+c_2Y^2)+aXY^2-bX^3/3$ with an additional nonpolynomial term $\mu Y^{-2}$ is known to be Liouville integrable for three sets of values of $(b/a,c_1,c_2)$. It has been previously integrated by genus two theta functions only in one of these cases. Defining the separating variables of the Hamilton-Jacobi equations, we succeed here, in the two other cases, to integrate the equations of motion with hyperelliptic functions.Comment: LaTex 2e. To appear, Journal of Mathematical Physic

A consideration of the effects of the slip displacement on fretting fatigue behaviour

Published versio

Remove Noise in Video with 3D Topological Maps

International audienceIn this paper we present a new method for foreground masks denoising in videos. Our main idea is to consider videos as 3D images and to deal with regions in these images. Denoising is thus simply achieved by merging foreground regions corresponding to noise with background regions. In this framework, the main question is the definition of a cri-terion allowing to decide if a region corresponds to noise or not. Thanks to our complete cellular description of 3D images, we can propose an advanced criterion based on Betti numbers, a topological invariant. Our results show the interest of our approach which gives better results than previous methods

The role of high-order phase correlations in texture processing

AbstractIsodipole textures are pairs of texture ensembles whose autocorrelations, and hence power spectra, are equal. Examples of readily discriminable isodipole textures are well known. Such discriminations appear to require feature extraction, since the isodipole condition eliminates ensemble differences in spatial frequency content. We studied the effects of phase decorrelation on VEP indices of discrimination of isodipole texture pairs. Phase decorrelation, which ranged from 0.125π radians (slight randomization) to π radians (complete randomization), was introduced in two ways: by independent jittering of each spatial Fourier component, and by a product method, which preserved correlations among certain quadruples of spatial Fourier components, despite pairwise decorrelation. For the even/random isodipole texture pair, independent phase decorrelation greater than 0.5π radians markedly reduced VEP indices of texture discrimination for all check sizes, and eliminated them entirely for check sizes of 8 min or greater. However, the product method preserved texture discrimination signals even with complete pairwise randomization of spatial phases. For the triangle/random isodipole texture pair, both kinds of phase decorrelation eliminated VEP indices of texture discrimination. These results imply that isodipole texture discrimination is based on fundamentally local processing, and not on global Fourier amplitudes—since the phase manipulations which eliminate texture discrimination preserve the Fourier amplitudes. The dependence of the antisymmetric response component (the odd harmonics) on phase decorrelation and texture type is consistent with a previously proposed model for feature extraction, and leads to constraints on how texture processing is modulated by contrast. The limited contribution of global spectral characteristics for small checks is consistent with a previously identified breakdown in scale-invariant processing