Social networks and trust: not the experimental evidence you may expect

We run a laboratory experiment where 'friendship' networks are generated endogenously within an anonymous group. Our experiment builds on two phases in sequence: a network formation game and a trust game. We find that in those sessions where the trust game is played before the network formation game, the overall level of trust is not significantly different from the one observed in a simple trust game; in those sessions where the trust game is played after the network formation game we find that the overall level of trust is significantly lower than in the simple trust game. Hence surprisingly trust does not increase because of 'enforced reciprocity' and moreover a common social history does affect the level of trust, but in a negative manner. Where network effects matter is in the choice of whom to trust: while we tend to trust less on average those with whom we have already interacted compared to total strangers, past history allows us to select whom to trust relatively more than others

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

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

Elective affinities

We propose a marriage model where assortative matching results in equilibrium for reasons other than those driving similar results in the search and matching literature. A marriage is a joint venture where husband and wife contribute to the couple’s welfare by allocating their time to portfolios of risky activities. Men and women are characterised by different preferences over risk and the optimal match is between partners with the same level of risk aversion. In our model no two men (women) rank the same woman (men) as most desirable. Given that there is no unanimous ranking of candidates, everyone marries in equilibrium their most preferred partne

Elective affinities

2noWe propose a marriage model where assortative matching results in equilibrium for reasons other than those driving similar results in the search and matching literature. A marriage is a joint venture where husband and wife contribute to the couple’.s welfare by allocating their time to portfolios of risky activities. Men and women are characterised by different preferences over risk and the optimal match is between partners with same level of risk aversion. In our model no two men (women) rank the same woman (men) as most desirable. Given that there is no unanimous ranking of candidates, everyone marries in equilibrium their most preferred partner.openopenD. Di Cagno; E. SciubbaDI CAGNO, DANIELA TERESA; E., Sciubb

Belief heterogeneity and survival in incomplete markets

In complete markets economies (Sandroni [16]), or in economies with Pareto optimal outcomes (Blume and Easley [10]), the market selection hypothesis holds, as long as traders have identical discount factors. Traders who survive must have beliefs that merge with the truth. We show that in incomplete markets, regardless of traders’ discount factors, the market selects for a range of beliefs, at least some of which do not merge with the truth. We also show that impatient traders with incorrect beliefs can survive and that these incorrect beliefs impact prices. These beliefs may be chosen so that they are far from the truth

TOPS project: Development of new fast timing plastic scintillators.

In particle physics charged particles are measured exploiting many different detection strategies. The plastic scintillators are cheap, versatile and show good time response, thus are traditionally employed as timing detectors. TOPS (Time Of flight Plastic Scintillators) is an R&D project devoted to the synthesis and characterization of a novel class of plastic scintillators. Liquid and solid sam- ples of tens of new scintillators have been tested and characterized. Some of them (2N, 1N, 2B, P2, T2) have shown a larger light output with respect to antracene, a standard benchmark material, and good timing properties. In order to improve the matching between the scintillators emission and the optimal trasmittive region in the absorption spectra, a doping material has been added as wave-shifter. The use of POPOP as doping improved the performances of a fraction of the scintillator samples. Based on the comparison of the light output values in measurements with cosmic rays, a selection of the most promising scintillators has been investigated also from the timing point of view. The scintillation time characteristics of the TOPS plastic samples have been studied with minimum ionizing particles using a commercial plastic scintillator BC-412 as a reference. The light output and timing properties have been also investigated with proton beams at different energies (70, 120, 170, 220 MeV) and show promising results providing a time of flight measure- ments accuracy of 150–300ps. In this contribution, preliminary results obtained with this new class of scintillators developed in the TOPS project will be presented

Measurement of secondary particle production induced by particle therapy ion beams impinging on a PMMA target

Particle therapy is a technique that uses accelerated charged ions for cancer treatment and combines a high irradiation precision with a high biological effectiveness in killing tumor cells [1]. Informations about the secondary particles emitted in the interaction of an ion beam with the patient during a treatment can be of great interest in order to monitor the dose deposition. For this purpose an experiment at the HIT (Heidelberg Ion-Beam Therapy Center) beam facility has been performed in order to measure fluxes and emission profiles of secondary particles produced in the interaction of therapeutic beams with a PMMA target. In this contribution some preliminary results about the emission profiles and the energy spectra of the detected secondaries will be presente

Performance of the Muon Identification at LHCb

The performance of the muon identification in LHCb is extracted from data using muons and hadrons produced in J/\psi->\mu\mu, \Lambda->p\pi and D^{\star}->\pi D0(K\pi) decays. The muon identification procedure is based on the pattern of hits in the muon chambers. A momentum dependent binary requirement is used to reduce the probability of hadrons to be misidentified as muons to the level of 1%, keeping the muon efficiency in the range of 95-98%. As further refinement, a likelihood is built for the muon and non-muon hypotheses. Adding a requirement on this likelihood that provides a total muon efficiency at the level of 93%, the hadron misidentification rates are below 0.6%.Comment: 17 pages, 10 figure