We present a dynamic model of endogenous interest group sizes and policymaking. The model integrates ‘top-down’ (policy) and ‘bottom-up’ (individual and social-structural) influences on the development of interest groups. Comparative statics results show that the standard assumption of fixed-sized interest groups can be misleading. Furthermore, dynamic analysis of the model demonstrates that re...

We develop a model of repeated microcredit lending to study how group size affects optimal group-lending contracts with joint liability. In the setting being studied, a benevolent lender provides microcredit to a group of borrowers to invest in projects. The outcome of each risky project is not observable by the lender; therefore, if some of the borrowers default on their loan repayments, the l...

In many contest situations, the number of participants is not observable at the time of investment. We design a laboratory experiment to study individual behavior in Tullock (lottery) contests with group size uncertainty. There is a fixed pool of n potential players, each with independent probability q ∈ (0, 1] of participating. As shown by Lim and Matros (2009; Games and Economic Behavior, vol...

Microbes produce many molecules that are important for their growth and development, and the exploitation of these secretions by nonproducers has recently become an important paradigm in microbial social evolution. Although the production of these public-goods molecules has been studied intensely, little is known of how the benefits accrued and the costs incurred depend on the quantity of publi...

Buggy Creek (BCR) virus is an arthropod-borne alphavirus that is naturally transmitted to its vertebrate host the cliff swallow (Petrochelidon pyrrhonota) by an invertebrate vector, namely the cimicid swallow bug (Oeciacus vicarius). We examined how the prevalence of the virus varied with the group size of both its vector and host. The study was conducted in southwestern Nebraska where cliff sw...

We analyze a model of a repeated microcredit lending and study how group size affects the optimal group lending contracts with joint liability. The story is that one benevolent lender gives microcredit to a group of n borrowers to be invested on n projects. The outcome of each risky project is not observable by the lender. Therefore in case some of the borrowers default on their loan repayments...

According to the Olson paradox, larger groups may be less successful than smaller groups in furthering their interests. We address the issue in a model with three distinctive features: explicit intergroup interaction, collective prizes with a varying mix of public and private characteristics, and nonlinear lobbying costs. The interplay of these features leads to new results. When the cost of lo...

Matching under transferable utility is well understood when groups of fixed size n = 2 are being formed: Complementarity or substitutability of types in the group payoff function pins down the matching pattern, whatever the distribution of types or specifics of the payoff function. But little is known about one-sided matching in the case of groups with fixed size n > 2. This subject is taken up...