Disposition, History and Contributions in Public Goods Experiments

Private incentives to invest in a public good are modeled as self- interested reciprocity where individuals use reputational scoring rules to determine their optimal level of investment. The model predicts that the disposition of any subject to cooperate is revealed by their first period investment in a voluntary contribution experiment, and that grouping cooperative subjects together will improve, and in some circumstances sustain, their private investment in the public good. Actual investment behavior is then studied with laboratory experiments that compare the contributions of subjects randomly reassigned into groups to contributions under a mechanism that sorts subjects into groups based on their individual investment decisions. The sorting mechanism helps to keep subjects with cooperative dispositions together and leads to statistically significant increases, relative to the random matching condition, in cooperators’ investments in the public good.public goods, experiments, cooperation, type classification, individual differences

Public Goods Agreements with Other-Regarding Preferences

Why cooperation occurs when noncooperation appears to be individually rational has been an issue in economics for at least a half century. In the 1960’s and 1970’s the context was cooperation in the prisoner’s dilemma game; in the 1980’s concern shifted to voluntary provision of public goods; in the 1990’s, the literature on coalition formation for public goods provision emerged, in the context of coalitions to provide transboundary pollution abatement. The problem is that theory suggests fairly low (even zero) levels of contributions to the public good and high levels of free riding. Experiments and empirical evidence suggests higher levels of cooperation. This is a major reason for the emergence in the 1990’s and more recently of the literature on other-regarding preferences (also known as social preferences). Such preferences tend to involve higher levels of cooperation (though not always). This paper contributes to the literature on coalitions, public good provision and other-regarding preferences. For standard preferences, the marginal per capita return (MPCR) to investing in the public good must be greater than one for contributing to be individually rational. We find that Charness-Rabin preferences tend to reduce this threshold for individual contributions. We also find that Charness-Rabin preferences reduce the equilibrium size of a coalition of agents formed to provide the public good. In contrast to much of the literature, we treat the wealth of agents as heterogeneous. In such cases, we find that transfers among agents of the coalition may be necessary to sustain cooperation (regardless of the nature of preferences). An example drawn from experiments is provided as an illustration of the effectiveness of social preferences.

Voting on Punishment Systems within a Heterogeneous Group

We consider a voluntary contributions game, in which players may punish others after contributions are made and observed. The productivity of contributions, as captured in the marginal-per-capita return, differs among individuals, so that there are two types: high and low productivity. Every two or eight periods, depending on the treatment, individuals vote on a punishment regime, in which certain individuals are permitted, but not required, to have punishment directed toward them. The punishment system can condition on type and contribution history. The results indicate that the most effective regime, in terms of contributions and earnings, is one that allows punishment of low contributors only, regardless of productivity. Nevertheless, only a minority of sessions converge to this system, indicating a tendency for the voting process to lead to suboptimal institutional choice.voting, punishment, voluntary contributions, heterogeneity, experiment

An Experimental Dynamic Public Goods Game with Carryover

We examine voluntary contributions in a two-stage public good experiment with ‘carryover.’ In two treatments, each subject’s second stage endowment is determined by the return from the public good in the first stage. We manipulate payoffs across these treatments so that, relative to our no-carryover baseline, earnings from either Nash play or Pareto Optimal play are held constant. The remaining two treatments maintain a constant endowment in each stage, but vary the marginal per capita return (MPCR) to contributions in the second stage. Our results indicate that carryover increases first stage contributions. Our implementation of carryover enables us to examine the effects of changing endowments and MPCR’s with a wider variety of parameter values than in the existing literature. Consistent with these studies, we find that MPCR and endowment effects are important determinants of subject contributions to the group account. While stage 1 contributions tend to increase in the presence of carryover, efficiency levels across both stages fall relative to the baseline due to the high potential payoffs from complete contribution in the second stage (due to higher endowments or MPCR levels).

\u3cem\u3eIn vitro\u3c/em\u3e Effect of Graphene Structures as an Osteoinductive Factor in Bone Tissue Engineering: A Systematic Review

Graphene and its derivatives have been well‐known as influential factors in differentiating stem/progenitor cells toward the osteoblastic lineage. However, there have been many controversies in the literature regarding the parameters effect on bone regeneration, including graphene concentration, size, type, dimension, hydrophilicity, functionalization, and composition. This study attempts to produce a comprehensive review regarding the given parameters and their effects on stimulating cell behaviors such as proliferation, viability, attachment and osteogenic differentiation. In this study, a systematic search of MEDLINE database was conducted for in vitro studies on the use of graphene and its derivatives for bone tissue engineering from January 2000 to February 2018, organized according to the PRISMA statement. According to reviewed articles, different graphene derivative, including graphene, graphene oxide (GO) and reduced graphene oxide (RGO) with mass ratio ≤1.5 wt % for all and concentration up to 50 μg/mL for graphene and GO, and 60 μg/mL for RGO, are considered to be safe for most cell types. However, these concentrations highly depend on the types of cells. It was discovered that graphene with lateral size less than 5 µm, along with GO and RGO with lateral dimension less than 1 µm decrease cell viability. In addition, the three‐dimensional structure of graphene can promote cell‐cell interaction, migration and proliferation. When graphene and its derivatives are incorporated with metals, polymers, and minerals, they frequently show promoted mechanical properties and bioactivity. Last, graphene and its derivatives have been found to increase the surface roughness and porosity, which can highly enhance cell adhesion and differentiation

Heterogeneous Productivity in Voluntary Public Good Provision: an Experimental Analysis

This article experimentally examines voluntary contributions when group members’ marginal returns to the public good vary. The experiment implements two marginal return types, low and high, and uses the information that members have about the heterogeneity to identify the applied contribution norm. We find that norms vary with the information environment. If agents are aware of the heterogeneity, contributions increase in general. However, high types contribute more than low types when contributions can be linked to the type of the donor but contribute less otherwise. Low types, on the other hand, contributes more than high types when group members are aware of the heterogeneity but contributions cannot be linked to types. Our results underline the importance of the information structure when persons with different abilities contribute to a joint project, as in the context of teamwork or charitable giving.Public Goods, Voluntary contribution mechanism, Heterogeneity, Information, Norms