The science and management of infectious disease are entering a new stage. Increasingly public policy to manage epidemics focuses on motivating people, through social distancing policies, to alter their behavior to reduce contacts and reduce public disease risk. Person-to-person contacts drive human disease dynamics. People value such contacts and are willing to accept some disease risk to gain contact-related benefits. The cost-benefit trade-offs that shape contact behavior, and hence the course of epidemics, are often only implicitly incorporated in epidemiological models. This approach creates difficulty in parsing out the effects of adaptive behavior. We use an epidemiological-economic model of disease dynamics to explicitly model the trade-offs that drive person-toperson contact decisions. Results indicate that including adaptive human behavior significantly changes the predicted course of epidemics and that this inclusion has implications for parameter estimation and interpretation and for the development of social distancing policies. Acknowledging adaptive behavior requires a shift in thinking about epidemiological processes and parameters.susceptible-infected-recovered model | R 0 | reproductive number | bioeconomics T he science and management of infectious disease is entering a new stage. The increasing focus on incentive structures to motivate people to engage in social distancing-reducing interpersonal contacts and hence public disease risk (1)-changes what health authorities need from epidemiological models. Social distancing is not new-for centuries humans quarantined infected individuals and shunned the obviously ill, but new approaches are being used to deal with modern social interactions. Scientific development of social distancing public policies requires that epidemiological models explicitly address behavioral responses to disease risk and other incentives affecting contact behavior. This paper models the role of adaptive behavior in an epidemiological system. Recognizing adaptive behavior means explicitly incorporating behavioral responses to disease risk and other incentives into epidemiological models (2, 3). The workhorse of modern epidemiology, the compartmental epidemiological model (4, 5), does not explicitly include behavioral responses to disease risk. The transmission factors in these models combine and confound human behavior and biological processes. We develop a simple compartmental model that explicitly incorporates adaptive behavior and show that this modification alters understanding of standard epidemiological metrics. For example, the basic reproductive number, R 0 , is a function of biological processes and human behavior, but R 0 lacks a behavioral interpretation in the existing literature. Biological and behavioral feedbacks muddle R 0 's biological interpretation and confound its estimation.Prior approaches that incorporate behavior into epidemiological models generally fall into three categories: specification of nonlinear contact rate functions, expanded epidemiologi...

Some small-holders are able to generate reliable and substantial income flows through small-scale dairy production for the local market; for others, a set of unique transaction costs hinders participation. Cooperative selling institutions are potential catalysts for mitigating these costs, stimulating entry into the market, and promoting growth in rural communities. Trends in cooperative organization in east-African dairy are evaluated. Empirical work focuses on alternative techniques for effecting participation among a representative sample of peri-urban milk producers in the Ethiopian highlands. The variables considered are a modern production practice (cross-bred cow use), a traditional production practice (indigenous-cow use), three intellectual-capital-forming variables (experience, education, and extension), and the provision of infrastructure (as measured by time to transport milk to market). A Tobit analysis of marketable surplus generates precise estimates of non-participants' 'distances' to market and their reservation levels of the covariatesmeasures of the inputs necessary to sustain and enhance the market. Policy implications focus on the availability of cross-bred stock and the level of market infrastructure, both of which have marked effects on participation, the velocity of transactions in the local community and, inevitably, the social returns to agroindustrialization. 0 cooperative sales organizations among resource-poor dairy producers in peri-urban settings.Small-scale dairy production is an important source of cash income for subsistence farmers in the east-African highlands. Dairy products are a traditional consumption item with strong demand, and the temperate climate allows the cross-breeding of local cows with European dairy breeds to raise productivity. Particularly where infrastructure and expertise in dairy processing exist, such markets 0169-5150/00/$ -see front matter 0 2000 Elsevier Science B.V. All rights reserved PII: S O l h 9 -5 1 5 0 ( 0 0 ) 0 0 0 8 9 -X

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Increasingly, spatial econometric methods are becoming part of the standard toolkit of applied researchers in agricultural, environmental and development economics. Nonetheless, applications in discrete-choice settings remain few and despite its appeal, applications of the Bayesian paradigm in these settings are still fewer. We provide a primer to the Bayesian spatial probit with the objective of making accessible to non-users a class of iterative estimation methods that have become fairly routine in Bayesian circles, offer an extremely powerful addition to applied researchers toolkits, and are essential in Bayesian implementation of spatial econometric models. We demonstrate the methods and apply them to estimate the 'neighbourhood effect' in high-yielding variety (HYV) adoption among Bangladeshi rice producers. We estimate the strength of this relationship using a standard, spatial probit model and compare the policy conclusions with and without the neighbourhood effect included. 0 2002 Published by Elsevier Science B.V. JEL rlass$cation: 013; 031 (G. Holloway).element, ignoring spatial relations can render conventional estimators inconsistent and/or biased. In some cases, spatial parameters also have important policy relevance. For example, the spatial autoregression parameter (the 'neighbourhood effect') in a technology adoption setting contains important policy information for public policy planning (Case, 1992). Knowledge of the location and scale of its distribution can be important in informing extension agents and planners about the likelihood that initial investments will generate further 'secondary' or 'copy' adoption in a locality. And this information, in turn, can aid decision making so that research portfolio and public investment schedules are optimised.One reason likely for the paucity of spatial discretechoice modelling is the complexity that it entails. Most of the available methods involve multidimensional 0169-5150/02/$ -see front matter 0 2002 hblished by Elsevier Science B.V. PII: S 0 1 6 9 -5 1 5 0 (0 2) 0 0 0 7 0 -1 384 G. Holloway et al. /Agricultural Economics 27 (2002) 383-402

Gardner's popular model of perfect competition in the marketing sector is extended to a conjectural-variations oligopoly with endogenous entry. Revising Gardner's comparative statics on the "farm-retail price ratio," tests of hypotheses about food industry conduct are derived. Using data from a recent article by Wohlgenanr, which employs Gardner's framework, tests are made of the validity of his maintained hypothesis-that the food industries are perfectly competitive. No evidence is found of departures from competition in the output markets of the food industries of eight commodity groups: (al beef and veal, (bl pork, (e) poultry, (d) eggs, (e) dairy, (f) processed fruits and vegetables, (g) fresh fruit. and (h) fresh vegetables.Key words: conjectural-variations oligopoly, farm-retail price ratio, food industry conduct.In a previous article in this JournaL, Gardner investigated the effects of three distinct forces affecting food system equilibria: shifts in retail demand, shifts in farm commodity supply, and shifts in marketing input supply. He derived comparative-static predictions about how the quotient of retail and farm prices-the "retailfarm price ratio~-would adjust to changes in each of these exogenous effects. The investigation was conducted within a framework that has since been applied to a number of important marketing system issues, including the quantification of downstream research benefits (Alston and Scobie; Freebairn, Davis, and Edwards), the characterization of marketing industry efficiency (Kilmer), and the incorporation of marketing group behavior in modeling the deGarth J.Weinberg. several Journal reviewers, and seminar participants at the University of California, Davis. mand for farm output (Wohlgenant). Yet, despite this clear popularity as a paradigm for food market analysis, the model's applicability is limited by a number of restrictive assumptions. Perhaps the most stringent of these assumptions is that of perfect competition in the food industries. Indeed, since Gardner's paper, an extensive literature has developed about the potentially noncompetitive conduct of firms in these industries (e.g., Gisser, Mueller and Marion, Connor et al.).Given the frequency of use of the Gardner framework, two questions arise for applied economic analysis, The first is how Gardner's model may be extended to allow for noncompetitive behavior in food marketing; the second is how some of Gardner's concepts may be applied to identify empirically departures from perfect competition. This paper investigates these issues by identifying the causes and consequences of noncompetitive conduct in the food industries, The specific objectives are to (a) provide a conceptual framework for the analysis of imperfect competition in these industries, (b) assess the analytical consequences of noncompetitive behavior, and (c) determine the empirical significance of such behavior.The first objective is achieved through an oligopolistic generalization of the Gardner model, which explicitly allows for the entry of new firms...