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This paper develops a consumption-based asset pricing model in which attitudes towards risk are contingent upon the state of the world. For a low high level of consumption relative to a subjective metric, counter-cyclical pro-cyclical risk aversion implies that consumption shocks generate larger uctuations in marginal utility, against which the agent will hedge in choosing his optimal portfolio. Asset prices are studied using two-state Markov preference regimes where bull and bear markets re ect alternating periods of low and high risk aversion. Joint estimation of bond and stock prices highlights moderate and infrequent m o v ements in risk aversion, and a marked improvement on the model's ability to capture the cyclical nature of observed asset prices.

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Office-based sutureless transconjunctival pars plana vitrectomy, with infusion when needed, is an effective operation for selected diseases of the posterior segment. In a multicenter series of 225 eyes, there were 15 complications in 14 (6%) eyes. Two of the complications were successfully managed with additional office procedures; one was managed in the operating room; and 12 resolved spontaneously.

SUMMARYWe provide a general methodology for forecasting in the presence of structural breaks induced by unpredictable changes to model parameters. Bayesian methods of learning and model comparison are used to derive a predictive density that takes into account the possibility that a break will occur before the next observation. Estimates for the posterior distribution of the most recent break are generated as a by-product of our procedure. We discuss the importance of using priors that accurately reflect the econometrician's opinions as to what constitutes a plausible forecast. Several applications to macroeconomic time-series data demonstrate the usefulness of our procedure.