On the Emergence of Cities

This paper considers the formation of cities in a simple model in which the preferences of agents depend on at most two characteristics of a location: its population and its average distance to the other agents. In such a simple model it is possible to recreate phenomena such as path dependency and centrally located cities which have been generated in more sophisticated models. Moreover, an example is provided in which cities emerge in the sense that the micro level preferences of agents do not appear to favor locating near or with other agents. When nonlinear effects are included then it is possible to show that even if efficient equilibria exist, they are not likely to occur and that there may exist extreme sensitivity to initial conditions. The model suggests that the mapping from individual preferences to population distributions merits further study

A Bottom-Up Efficient Algorithm for Allocating Public Projects with Positive Complementarities

In this paper, we consider the problem of locating an optimal package of public projects from a set of potential projects when the public projects have positive complementarities. We formulate the problem as a discrete nonlinear optimization problem whose domain equals the power set of a finite collection of projects. The main contribution of this paper is the construction of an efficient algorithm, among the set of bottom-up algorithms, for projects with positive and positive uniform complementarities. The restriction to bottom-up algorithms sterns from practical considerations discussed in the paper. We also discuss shortcomings of three natural approaches to addressing the problem: exhaustive search over packages, simultaneous evaluation of projects, and sequential evaluation of projects

Covers

This paper introduces the theory of covers for functions defined over binary variables. Covers formalize the notion of decomposability. Large complex problems are decomposed into subproblems each containing fewer variables, which can then be solved in parallel. Practical applications of the benefits from decomposition include the parallel architecture of supercomputers, the divisionalization of firms, and the decentralization of economic activity. In this introductory paper, we show how covers also shed light on the choice among public projects with complementarities. Further, covers provide a measure of complexity/decomposability with respect to contour sets, allowing for nonlinear effects which occur near the optimum to receive more weight than nonlinear effects arbitrarily located in the domain. Finally, as we demonstrate, covers can be used to analyze and to calibrate search algorithms

Optimal team composition for tool‐based problem solving

In this paper, we construct a framework for modeling teams of agents who apply techniques or procedures (tools) to solve problems. In our framework, tools differ in their likelihood of solving the problem at hand; agents, who may be of different types, vary in their skill at using tools. We establish baseline hiring rules when a manager can dictate tool choice and then derive results for strategic tool choice by team members. We highlight three main findings: First, that cognitively diverse teams are more likely to solve problems in both settings. Second, that teams consisting of types that master diverse tools have an indirect strategic advantage because tool diversity facilitates coordination. Third, that strategic tool choice creates counterintuitive optimal hiring practices. For example, optimal teams may exclude the highest ability types and can include dominated types. In addition, optimal groups need not increase setwise. Our framework extends to cover teamwork on decomposable problems, to cases where individuals apply multiple tools, and to teams facing a flow or set of problems.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152035/1/jems12295.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152035/2/jems12295_am.pd

First mover or higher quality? Optimal product strategy in markets with positive feedbacks

Conventional wisdom holds that in markets with positive feedbacks being first to market can matter more than product quality. In this paper, we test that intuition within a generalized Pólya urn model. We find that if we assume constant feedbacks, in the long run, higher quality products dominate the market regardless of initial market shares, contradicting the common wisdom. However, when we allow for variable feedbacks, initial advantages persist almost indefinitely. Thus, the choice of whether to rush to market or focus on quality depends on market characteristics such as whether the positive feedbacks result from more consistent returns to scale or from more variable social influences.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142337/1/jems12231-sup-0001-OnlineAppendix.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142337/2/jems12231_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142337/3/jems12231.pd

The Complexities of Global Systems History*

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79129/1/j.1540-5923.2010.00307.x.pd

Current understandings of sex-based harassment and stalking perpetration

Sex-based harassment and stalking are highly prevalent forms of interpersonal aggression that often result in an array of detrimental and severe impacts for victims. In this chapter, we examine some of the common challenges associated with defining and legislating against sex-based harassment and stalking, as well as considering existing classifications of behaviour and perpetrator motivations. In doing so, our aim is to highlight the complex nature of these forms of interpersonal aggression and the difficulties associated with ascertaining boundaries between ‘reasonable’ and ‘unreasonable’ behaviour. We proceed to discuss the importance of appropriately targeted evidence-based educational campaigns to increase public awareness and understanding regarding the reality of sex-based harassment and stalking. Our conclusion is that increased education will enable greater recognition of the diverse behaviours that constitute sex-based harassment and stalking, so that people are better able to identify both their own and others’ victimisation experiences

Diversity-induced resonance in a system of globally coupled linear oscillators

The purpose of this paper to analyze in some detail the arguably simplest case of diversity-induced reseonance: that of a system of globally-coupled linear oscillators subjected to a periodic forcing. Diversity appears as the parameters characterizing each oscillator, namely its mass, internal frequency and damping coefficient are drawn from a probability distribution. The main ingredients for the diversity-induced-resonance phenomenon are present in this system as the oscillators display a variability in the individual responses but are induced, by the coupling, to synchronize their responses. A steady state solution for this model is obtained. We also determine the conditions under which it is possible to find a resonance effect.Comment: Reported at the XI International Workshop "Instabilities and Nonequilibrium Structures" Vina del Mar (Chile

Improving College Access in the United States: Barriers and Policy Responses

Socioeconomic gaps in college enrollment and attainment have widened over time, despite increasing returns to postsecondary education and significant policy efforts to improve access. We describe the barriers that students face during the transition to college and review the evidence on potential policy solutions. We focus primarily on research that examines causal relationships using experimental or quasi-experimental methods, though we draw upon descriptive evidence to provide context. Our review is distinctive in three respects. First, in addition to the literature on financial aid, we examine the evidence on informational and behavioral interventions, academic programs, and affirmative action policies intended to improve college access. Second, we incorporate a wealth of recent research not included in prior reviews. Finally, we conceptualize college access broadly, as including not just whether but also where students attend and whether they have access to college-level courses. We conclude with a discussion of implications for policy and research