The firm and managerial misdirection of worker effort

This article models how a level of management between workers and the owner of a firm can affect the owner's decision either to internally integrate a function to make inputs or to contract out to buy inputs from an independent supplier. In the model, a self-serving manager can direct her workers to perform activities that serve her interests rather than those of the firm. This reduces the effectiveness of worker performance incentives intended to promote efforts that benefit the owner. Incentives may have to be increased to a level such that the owner prefers to buy inputs rather than make them internally.     

Market stability: backward-bending supply in a laboratory experimental market. 1999 Presidential address Western Economic Association

This article investigates the stability properties of markets with backward-bending supply curves. Parameters are chosen so that the two classic models of price dynamics, the Walrasian model and the Marshallian model, give opposite predictions. The results are (1) market instability can be observed, and (2) in the backward-bending case stability is captured by the Walrasian model and the Marshallian model of dynamics is rejected. Previous experiments have demonstrated that the Marshallian model works in the forward-falling case. Thus, which theory of dynamics is appropriate for a market depends on the underlying reasons for demand and supply shapes.     

Homophily and Contagion Are Generically Confounded in Observational Social Network Studies

The authors consider processes on social networks that can potentially involve three factors: homophily, or the formation of social ties due to matching individual traits; social contagion, also known as social influence; and the causal effect of an individual's covariates on his or her behavior or other measurable responses. The authors show that generically, all of these are confounded with each other. Distinguishing them from one another requires strong assumptions on the parametrization of the social process or on the adequacy of the covariates used (or both). In particular the authors demonstrate, with simple examples, that asymmetries in regression coefficients cannot identify causal effects and that very simple models of imitation (a form of social contagion) can produce substantial correlations between an individual's enduring traits and his or her choices, even when there is no intrinsic affinity between them. The authors also suggest some possible constructive responses to these results.     

Approximate Methods for State-Space Models

State-space models provide an important body of techniques for analyzing time-series, but their use requires estimating unobserved states. The optimal estimate of the state is its conditional expectation given the observation histories, and computing this expectation is hard when there are nonlinearities. Existing filtering methods, including sequential Monte Carlo, tend to be either inaccurate or slow. In this paper, we study a nonlinear filter for nonlinear/non-Gaussian state-space models, which uses Laplace's method, an asymptotic series expansion, to approximate the state's conditional mean and variance, together with a Gaussian conditional distribution. This Laplace-Gaussian filter (LGF) gives fast, recursive, deterministic state estimates, with an error which is set by the stochastic characteristics of the model and is, we show, stable over time. We illustrate the estimation ability of the LGF by applying it to the problem of neural decoding and compare it to sequential Monte Carlo both in simulations and with real data. We find that the LGF can deliver superior results in a small fraction of the computing time.     

Balance of care—a user's view of a new approach to joint strategic planning

Planning for care of the Elderly has to face the problems of an increasing elderly population; a wide range of alternative ways of caring for them (at widely differing costs); the fact that services are provided by several different organisations all facing difficult financial constraints; a range of professional opinion about the desirability or otherwise of alternative patterns of care and use of resources; a lack of data on how care is at present distributed; the lack of a structure for organising such data as are available; and the lack of an appropriate computer-based model for manipulating the large number of data elements necessary to describe and help to evaluate alternative plans for the future. The Balance of Care approach to the Joint Strategic Planning of Health and Social Services provision for the Elderly, is being used in pilot applications in two Areas in the UK. Its contribution to the solution of the problems outlined above is described by authors from the two Areas. The approach and the underlying model can be extended to strategic planning for other client groups requiring non-acute care.