4,688,476 research outputs found

    Group lending with endogenous group size

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    This paper focuses on the size of the borrower group in group lending. We show that, when social ties in a community enhance borrowers' incentives to exert effort, a profit-maximizing financier chooses a group of limited size. Borrowers that would be fundable under moral hazard but have insufficient social ties do not receive funding. The result arises because there is a trade-off between raising profits through increased group size and providing incentives for borrowers with less social ties. The result may explain why many micro-lending institutions and rural credit cooperatives lend to groups of small size.Group Lending; Moral Hazard; Social Capital

    Illusory correlation, group size and memory

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    Two studies were conducted to test the predictions of a multi-component model of distinctiveness-based illusory correlation (IC) regarding the use of episodic and evaluative information in the production of the phenomenon. Extending on the standard paradigm, participants were presented with 4 groups decreasing in size, but all exhibiting the same ratio of positive to negative behaviours. Study 1 (N = 75) specifically tested the role of group size and distinctiveness, by including a zero-frequency cell in the design. Consistent with predictions drawn from the proposed model, with decreasing group size, the magnitude of the IC effect showed a linear in- crease in judgments thought to be based on evaluative information. In Study 2 (N = 43), a number of changes were introduced to a group assignment task (double presentation, inclusion of decoys) that allowed a more rig- orous test of the predicted item-specific memory effects. In addition, a new multilevel, mixed logistic regression approach to signal-detection type analysis was used, providing a more flexible and reliable analysis than previ- ously. Again, with decreasing group size, IC effects showed the predicted monotonic increase on the measures (group assignment frequencies, likability ratings) thought to be dependent on evaluative information. At the same time, measures thought to be based on episodic information (free recall and group assignment accuracy) partly revealed the predicted enhanced episodic memory for smaller groups and negative items, while also supporting a distinctiveness-based approach. Additional analysis revealed that the pattern of results for judg- ments though to be based on evaluative information was independent of interpersonal variation in behavioral memory, as predicted by the multi-component model, and in contrast to predictions of the competing models. The results are discussed in terms of the implications of the findings for the proposed mechanisms of illusory correlation

    Group Testing with Pools of Fixed Size

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    In the classical combinatorial (adaptive) group testing problem, one is given two integers dd and nn, where 0dn0\le d\le n, and a population of nn items, exactly dd of which are known to be defective. The question is to devise an optimal sequential algorithm that, at each step, tests a subset of the population and determines whether such subset is contaminated (i.e. contains defective items) or otherwise. The problem is solved only when the dd defective items are identified. The minimum number of steps that an optimal sequential algorithm takes in general (i.e. in the worst case) to solve the problem is denoted by M(d,n)M(d, n). The computation of M(d,n)M(d, n) appears to be very difficult and a general formula is known only for d=1d = 1. We consider here a variant of the original problem, where the size of the subsets to be tested is restricted to be a fixed positive integer kk. The corresponding minimum number of tests by a sequential optimal algorithm is denoted by M[k](d,n)M^{\lbrack k\rbrack}(d, n). In this paper we start the investigation of the function M[k](d,n)M^{\lbrack k\rbrack}(d, n)

    Synergy and Group Size in Microbial Cooperation

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    Microbes produce many molecules that are important for their growth and development, and the consumption of these secretions by nonproducers has recently become an important paradigm in microbial social evolution. Though the production of these public goods molecules has been studied intensely, little is known of how the benefits accrued and costs incurred depend on the quantity of public good molecules produced. We focus here on the relationship between the shape of the benefit curve and cellular density with a model assuming three types of benefit functions: diminishing, accelerating, and sigmoidal (accelerating then diminishing). We classify the latter two as being synergistic and argue that sigmoidal curves are common in microbial systems. Synergistic benefit curves interact with group sizes to give very different expected evolutionary dynamics. In particular, we show that whether or not and to what extent microbes evolve to produce public goods depends strongly on group size. We show that synergy can create an “evolutionary trap” which can stymie the establishment and maintenance of cooperation. By allowing density dependent regulation of production (quorum sensing), we show how this trap may be avoided. We discuss the implications of our results for experimental design

    Informal Insurance with Endogenous Group Size

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    We present a theory of endogenous formation of insurance groups which combines heterogeneity on agents' risk aversion under asymmetric information and lack of enforceability of contracts. Income sharing inside the group is decided by majority voting and the size of the group adjusts to this decision through participation constraints. At equilibrium, all group members agree on the same imperfect level of income sharing, which yields a constrained-efficient equilibrium. Comparative statics on the risk faced by the community provide interesting results. A mean preserving spread of income implies more income sharing and a larger group size. New members, and possibly even old members may be better o¤, while non-members are worse-o¤. These results have relevant policy implications.

    Group size, Grooming and Social Cohesion in Primates

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    Most primates live in social groups in which affiliative bonds exist between individuals. Because these bonds need to be maintained through social interactions (grooming in most primates), sociality will be limited by time constraints. It has previously been shown that the time primates invest in grooming increases with group size. However, when groups become too large, individuals will not have enough time available to service all possible social relationships and group cohesion is expected to decrease. In this study, we used data from previously published studies to determine how large groups compromise on their grooming time and how ecological, phylogenetic and life history variables affect time invested in grooming (across species as well as within taxa). We used path analysis to analyse direct and indirect (via group size) effects on grooming. We showed that not only is grooming time determined by group size, but it is also affected by dispersal patterns and sex ratio. Furthermore, we found that grooming time is asymptotic when group size exceeds 40 individuals, indicating that time constraints resulting from ecological pressure force individuals to compromise on their grooming time. This was true across species, but a similar effect was also found within taxa. Cognitive constraints and predation pressure strongly affect group sizes and thereby have an indirect effect on primate grooming time. Primates that were found to live in groups larger than predicted by their neocortex size usually suffered from greater predation risk. However, most populations in our analysis were placed well within what we define as their eco-cognitive niche. © 2007 The Association for the Study of Animal Behaviour

    Modulation of aggression in male mice: influence of group size and cage size

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    Aggression in group-housed male mice is known to be influenced by both cage size and group size. However, the interdependency of these two parameters has not been studied yet. In this study, the level of aggression in groups of three, five, or eight male BALB/c mice housed in cages with a floor size of either 80 or 125 cm2/animal was estimated weekly after cage cleaning for a period of 14 weeks. Furthermore, urine corticosterone levels, food and water intake, body weight, and number of wounds were measured weekly. At the end of the experiment, tyrosine hydroxylase (TH) activity, testosterone levels, and weight of spleen, thymus, testes, and seminal vesicles were determined. Results indicate a moderate increase of intermale aggression in larger cages when compared to the smaller cages. Aggression in groups of eight animals was considerably higher than in groups of three animals. The increase of agonistic behavior was observed both in dominant and subordinate animals. Physiological parameters indicate differences in stress levels between dominant and subordinate animals. It is concluded that aggressive behavior in group-housed male BALB/c mice is best prevented by housing the animals in small groups of three to five animals, while decreasing floor size per animal may be used as a temporary solution to decrease high levels of aggression in an existing social group.

    Free Riding on Altruism and Group Size

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    It is shown that altruism does not affect the equilibrium provision of public goods although altruism takes the form of unconditional commitment to contribute. The reason is that altruistic contributions completely crowd out selfish contributions. That is, egoists free ride on altruism. It is also shown that public goods are less likely to be provided in larger groups.Free Riding, Public good, Altruism
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