Working papers results

The triplet-based risk analysis of Kaplan and Garrick (1981) is the keystone of state-of-the-art probabilistic risk assesment in several applied fields. This paper performs a sharp embedding of the elements of this framework into the one of formal decision theory, which is mainly con- cerned with the methodological and modelling issues of rational decision making. In order to show the applicability of such an embedding, we also explicitly develop it within a nuclear probabilistic risk assessment, as prescribed by the U.S. NRC. The aim of this exercise is twofold: on the one hand, it gives risk analysis a direct access to the rich toolbox that decision theory has developed, in the last decades, in order to deal with complex layers of uncertainty; on the other, it exposes decision theory to the challenges of risk analysis, thus providing it with broader scope and new stimuli.

Government spending at the zero lower bound (ZLB) is not necessarily welfare enhancing, even when its output multiplier is large. We illustrate this point in the context of a standard New Keynesian model. In that model, when government spending provides direct utility to the household, its optimal level is at most 0.5- 1 percent of GDP for recessions of -4 percent; the numbers are higher for deeper recessions. When spending does not provide direct utility, it is generically welfare- detrimental: it should be kept unchanged at a long run-optimal value. These results are confirmed in a medium-scale DSGE version of the model featuring sticky wages and equilibrium unemployment.

This paper tests the commonly-used assumption that people apply a single discount rate to the utility from different sources of consumption. Using survey data from Uganda with both hypothetical and incentivized choices over different goods, we elicit time preferences from about 2,400 subjects. We reject the null of equal discount rates across goods; the average person in our sample is more impatient about sugar, meat and starchy plantains than about money and a list of other goods. We review theassumptions to recover discount rates from experimental choices for the case of goodspecific discounting. Consistently with the theoretical framework, we find convergence in discount rates across goods for two groups expected to engage in or think about arbitraging the rewards: traders and individuals with large quantities of the good at home. As an application, we evaluate empirically the conditions under which goodspecific discounting could predict a low-asset poverty trap.

We study decision problems in which the consequences of the alternative actions depend on states determined by a generative mechanism representing some natural or social phenomenon. Model uncertainty arises as decision makers may not know such mechanism. Two types of uncertainty result, a state uncertainty within models and a model uncertainty across them. We discuss some two-stage static decision criteria proposed in the literature that address state uncertainty in the first stage and model uncertainty in the second one (by considering subjective probabilities over models). We consider two approaches to the Ellsberg-type phenomena that these decision problems feature: a Bayesian approach based on the distinction between subjective attitudes toward the two kinds of uncertainty, and a non Bayesian one that permits multiple subjective probabilities. Several applications are used to illustrate concepts as they are introduced.

We prove that a subtle but substantial bias exists in a standard measure of the conditional dependence of present outcomes on streaks of past outcomes in sequential data. The magnitude of this novel form of selection bias generally decreases as the sequence gets longer, but increases in streak length, and remains substantial for a range of sequence lengths often used in empirical work. The bias has important implications for the literature that investigates incorrect beliefs in sequential decision making - most notably the Hot Hand Fallacy and the Gambler's Fallacy. Upon correcting for the bias, the conclusions of prominent studies in the hot hand fallacy literature are reversed. The bias also provides a novel structural explanation for how belief in the law of small numbers can persist in the face of experience.

We study optimal selling strategies of a seller who is poorly informed about the buyer's value for the object. When the maxmin seller only knows that the mean of the distribution of the buyer's valuations belongs to some interval then nature can keep him to payoff zero no matter how much information the seller has about the mean. However, when the seller has information about the mean and the variance, or the mean and the upper bound of the support, the seller optimally commits to a randomization over prices and obtains a strictly positive payoff. In such a case additional information about the mean and/or the variance affects his payoff.

This paper proposes a Bayesian estimation framework for a typical multi-factor model with timevarying risk exposures to macroeconomic risk factors and corresponding premia to price U.S. publicly traded assets. The model assumes that risk exposures and idiosynchratic volatility follow a break-point latent process, allowing for changes at any point on time but not restricting them to change at all points. The empirical application to 40 years of U.S. data and 23 portfolios shows that the approach yields sensible results compared to previous two-step methods based on naive recursive estimation schemes, as well as a set of alternative model restrictions. A variance decomposition test shows that although most of the predictable variation comes from the market risk premium, a number of additional macroeconomic risks, including real output and inflation shocks, are significantly priced in the cross-section. A Bayes factor analysis massively favors of the proposed change-point model.

We characterize the consistency of a large class of nonexpected utility preferences (including mean-variance preferences and prospect theory preferences) with stochastic orders (for example, stochastic dominances of different degrees). Our characterization rests on a novel decision theoretic result that provides a behavioral interpretation of the set of all derivatives of the functional representing the decision maker's preferences. As an illustration, we consider in some detail prospect theory and choice-acclimating preferences, two popular models of reference dependence under risk, and we show the incompatibility of loss aversion with prudence.

The hot hand fallacy refers to a belief in the atypical clustering of successes in sequential outcomes when there is none. It has long been considered a massive and widespread cognitive illusion with important implications in economics and finance. The strongest evidence in support of the fallacy remains that from the canonical domain of basketball, where the widespread belief in the existence of hot hand shooting, among expert players and coaches, has been found to have no evidential basis (Gilovich, Vallone, and Tversky 1985). A prominent exhibit of the fallacy is Koehler and Conley (2003)'s study of the NBA Three-Point Contest (1994-1997), a setting which is viewed as ideal for a test of the hot hand (Thaler and Sunstein 2008). In this setting, despite the well-known beliefs of players, coaches, and fans alike, Koehler and Conley find no evidence of hot hand shooting. In the present study, we collect 29 years of shooting data from television broadcasts of the NBA Three-Point Contest (1986-2015), and apply a statistical approach developed in Miller and Sanjurjo (2014), which is more powered, contains an improved set of statistical measures, and corrects for a substantial downward bias in previous estimates of the hot hand effect. In contrast with previous studies, but consistent with Miller and Sanjurjo (2014)'s recent finding of substantial hot hand shooting in all previous controlled shooting studies (including that from the original study of Gilovich, Vallone, and Tversky), we find substantial evidence of hot hand shooting in the NBA Three-Point Contest. This leaves little doubt that the hot hand not only exists, but actually occurs regularly. Thus, belief in the hot hand, in principle, is not a fallacy.

Exploiting the timing of the 2005-2006 Italian bankruptcy law reforms, we disentangle the effects of reorganization and liquidation in bankruptcy on bank financing nd firm investment. A 2005 reform introduces reorganization procedures facilitating loan renegotiation. The 2006 reform subsequently strengthens creditor rights in liquidation. The first reform increases interest rates and reduces investment. The second reform reduces interest rates and spurs investment. Our results highlight the importance of identifying the distinct effects of liquidation and reorganization, as these procedures differently address the tension in bankruptcy law between the continuation of viable businesses and the preservation of repayment incentives.