Consequences of irreversibilities on optimal intertemporal CO2 emission policies under uncertainty

This paper investigates how irreversibilities affect the optimal intertemporal accumulation of greenhouse gases in the atmosphere under uncertainty. More precisely, the evolution of the future temperature is assumed to follow an Itô-process with the drift provided by greenhouse gas emissions. This paper considers two different kinds of irreversibilities: of emissions (i.e., CO₂ once dissolved into the air cannot be collected later) and of stopping. These issues are investigated first (in the tradition of the real option literature) as pure stopping problems and then allowing for a continuous choice of emissions. Implications for global warming are: an irreversible stopping of greenhouse gas emissions is never optimal in a continuous framework and yields in the real option framework a less conservationist stopping rule in which uncertainty increases the stopping threshold (i.e. works against conservation).     

On preserving the reservation wage property in a continuous job search model

The purpose of this article is to examine a continuous model of job search. Job offers are received randomly over time according to a renewal process. The wage offers are assumed to be positive, independent, and identically distributed random variables. There is a search cost of c monetary units per unit time. The only decision the searcher must make is when to stop searching and accept an offer. It is shown that the optimal stopping strategy which maximizes the searcher's expected net return over the class of all stopping times possesses the reservation wage property, provided that the interarrival time between two successive job offers in NBUE (new better than used in expectation).     

A solution to a class of sequential decision problems

This paper presents an extension to standard results on optimal stopping rules for a class of search problems in which some attributes of interest to the searcher are not revealed during the search process. The suggested solution takes the form of a two-stage decision process.     

Risk aversion,impatience, and optimal timing decisions

In this paper, a theory measuring a decision maker's aversion to temporal risks is developed in the context of a simple choice framework that admits the interpretation “time varying utility of wealth.” A relation “more temporally risk averse” is defined and characterized in terms of instantaneous risk aversion (the usual single variable case) and impatience. A further characterization of this relation is obtained in the context of a class of action timing problems known as optimal stopping problems and is applied to preference based investigations of information production, incentives to innovate, and job search.     

Repeated Experimentation to Learn About a Flow-Pollutant Threshold

We examine in discrete time the management of a flow pollutant that causes damage when it crosses a fixed but unknown threshold. The manager sequentially chooses a pollution level that allows learning about the threshold, thereby improving future decisions. If crossed, damage can be reversed at some cost. We analyze the conditions under which experimentation is optimal, and explore how experimentation depends on restoration costs, information about the threshold, and the discount rate. Our results suggest that the level of experimentation, defined as the difference between the optimal activity with and without learning, is non-monotonic in costs and decreasing in the discount rate. We identify two stopping boundaries for the experiment, depending on cost levels compared to the lower bound of the threshold’s interval. We show that when costs are high the stopping boundary under an infinite number of decisions is the same as when there are only two decision moments. A computational extension to more than two decisions suggests that an optimal sequence of experiments can cross the same threshold several times before experimentation ceases. These results shed light on a large class of environmental decision problems that has not been examined in the literature.     

Urban job creation and unemployment in LDCs: Todaro vs. Harris and Todaro

Overwhelming urban migration occurred so rapidly in many developing countries that widespread unemployment and squalid living conditions are commonplace. For many of these countries, stopping urban migration has become a major policy. Two models propose 2 different theories of urban unemployment. Todaro's short-term effects model concludes that job creation actually causes unemployment. Todaro and Harris formulated a long-term effects model in which welfare subsidies create more employment and stimulate the economy. A real solution to urban job creation would include optimal allocation of investment between the rural and labor sectors. A once and for all hiring tax would reduce replacement hiring. It is impossible to design an optimal tax subsidy package for urban unemployment unless it includes knowledge of the dynamic response of migration and unemployment to the rate of net and gross hiring of labor. If subsidy taxes are levied on the agricultural sector, the net result may be a higher rate of capital formation in the (low social return) manufacturing sector and a lower one in the agricultural sector.     

Optimal stopping time with stochastic volatility

This paper demonstrates how to convert a path-dependent optimal stopping time problem into a path-independent problem using a transformation analysis method. We test this method to deal with several problems, especially those in stochastic volatility environments. We introduce stochastic state variables into volatility dynamics and analyse the influence of state-variable volatile characters on investment stopping boundaries. For arbitrary coefficient circumstances, we set up a Riccati equation that satisfies the transformation. For circumstances involving Heston stochastic-volatility, we propose an analytical solution. This paper extends research on the optimal investment stopping issue to a stochastic investment opportunity environment. Our proposed method can enhance the ability of optimal investment stopping theory to describe the real capital market.     

Applications of Optimal Stopping in Resource Economics*

Some applications of optimal stopping rules in the analysis of resource economic problems are surveyed. The conceptual foundation for the approach stems from the dual roles of uncertainty and irreversibility in these problems. A stochastic adaptation of Wicksell's ‘tree-cutting’ paradigm is exposited and shown to provide a rigorous methodology that is as intuitive as more familiar contingent-asset approaches. Four resource economic applications are considered: environmental problems, urban development, bioeconomic harvesting and resource project timing and valuation.     

Solving optimal timing problems in environmental economics

Two papers of Pindyck, 2000, Pindyck, 2002 that modeled the control of stock pollutants as optimal stopping problems contained closed form solutions that are incorrect. This paper discusses a subtle error in the derivation and demonstrates how solutions to these and related problems can be obtained numerically. The numerical solutions are contrasted with the ones contained in Pindyck's original papers.     

On optimal cycles in dynamic programming models with convex return function

Summary. In this paper we study the behavior of optimal paths in dynamic programming models with a strictly convex return function. Such a model has been investigated in Dawid and Kopel (1997) who assume that the growth of a renewable resource is governed by a piecewise linear function. We prove that in their model the optimal cycles undergo the following qualitative changes or bifurcations: a cycle of period n“bifurcates” into a cycle of period n+1 for increasing elasticity of the return function. We also show that under the assumption of a concave differentiable growth function the qualitative properties of the optimal policy remain valid: oscillating behavior is optimal. Furthermore, we demonstrate numerically that the period of a cyclic optimal path increases if the convexity of the return function (measured by the elasticity) increases. Received: January 22, 1997; revised version: October 13, 1997     

The Complementarity Of Mass Customization And Electronic Commerce

In this technology-intensive business world, it is important to note that technology does not work alone; it only works when all other supporting elements work in concert. Two ‘things’, or business strategies, are complementary when the marginal contribution of one increases with the value of the other, and vice versa This paper models two business strategies, electronic commerce and mass customization, in a profit maximization model and shows that these two strategies as complementary under certain assumptions. In doing so, this paper sheds light on why many mass customization attempts failed and why electronic commerce does not bring in as high a return as expected. This paper includes three sub-models and shows the optimal price movements under each scenario.     

Optimal diversification and risk-taking: a theoretical and empirical analysis

Among the justifications for capital property income received by private households is that it is a ‘return to risk-taking’. However, portfolio diversification provides an obvious means toward the reduction of risk. Moreover, it is widely believed that the wealthier the household, the more diversification it practices: the larger tends to be the proportion of its total portfolio allocated to publicly traded stock, and the larger tends to be the number of individual stock issues included in its portfolio. Using a simple ‘homogeneous securities’ model, explicit functional forms are obtained for both the optimal proportion of the portfolio allocated to stocks, and the optimal number of individual stock issues in the portfolio. Empirical evaluation of these theoretical results, using a dataset derived from the 2004 Survey of Consumer Finances (SCF), lends substantial support to the model. Applying these empirical results, it is found that as household capital wealth increases, expected capital income increases while simultaneously a reasonable risk indicator (the probability of incurring a negative return on the capital portfolio) decreases owing to the higher level of portfolio diversification. This indication casts significant doubt on the ‘return to risk-taking’ justification for capital property income received by wealthy private households.     

Optimal collusion-resistant mechanisms with verification

We present the first general positive result on the construction of collusion-resistant mechanisms, that is, mechanisms that guarantee dominant strategies even when agents can form arbitrary coalitions and exchange compensations (sometimes referred to as transferable utilities or side payments). This is a much stronger solution concept as compared to truthful or even group strategyproof mechanisms, and only impossibility results were known for this type of mechanisms in the “classical” model.We describe collusion-resistant mechanisms with verification that return optimal solutions for a wide class of mechanism design problems (which includes utilitarian ones as a special case). Note that every collusion-resistant mechanism without verification must have an unbounded approximation factor and, in general, optimal solutions cannot be obtained even if we content ourselves with truthful (“non-collusion-resistant”) mechanisms. All these results apply to problems that have been extensively studied in the algorithmic mechanism design literature like, for instance, task scheduling and inter-domain routing.     

The impact of recent mental health changes on employment: new evidence from longitudinal data

This study uses longitudinal data and four different measures of mental health to tease out the impact of psychiatric disorder onsets and recoveries on employment outcomes. Results suggest that developing a mental health problem leads to a significant increase in the probability of transitioning to non-employment, while a recovery increases the probability of return to work among the not employed with a mental health problem. No consistent effect was found on hours worked and earnings. Research and policy attention is needed with respect to early interventions such as job retention programmes to help workers with mental health problems remain employed as well as interventions that may lead to recovery and return to work. More research is needed especially with data and models that can differentiate between the effects of mental health onsets and recoveries on employment exit and return to work transitions.     

资本回报率增长的最优知识产权保护强度研究——基于82个国家面板数据的实证

基于制度层面分析资本回报率变动的动因有助于探索经济增长新动力。计算82个国家的资本回报率，并基于知识产权保护视角对其变动机制进行分析，得出以下主要结论：①资本回报率增长存在最优知识产权保护强度，但发展中国家的理论最优强度小于发达国家；②发展中国家知识产权保护以远离最优强度状态促进资本回报率提升，发达国家则以接近最优强度状态促进资本回报率提升；③金融危机后，知识产权保护的促进效应在发展中国家更加明显，在发达国家有所弱化；④机制分析显示，知识产权保护通过促进技术创新提升资本回报率。     

Financial Intermediation with Risk Aversion

The paper extends Diamond's (1984) analysis of financial intermediation to allow for risk aversion of the intermediary. As in the case of risk neutrality, the agency costs of external funds provided to an intermediary are relatively small if the intermediary is financing many entrepreneurs with independent returns. Even though the intermediary is adding rather than subdividing risks, the underlying large-numbers argument is not invalidated by the presence of risk aversion.
With risk aversion of entrepreneurs as well as the intermediary, financial intermediation provides insurance as well as finance. In contrast to earlier results on optimal intermediation policies under risk neutrality, the paper shows that when an intermediary is financing many entrepreneurs with independent returns, optimal intermediation policies must shift return risks away from risk averse entrepreneurs and impose them on the intermediary or on final investors.     

Investment Incentives of a Regulated Dominant Firm

We study the investment incentives of a regulated, incumbent firm in a deregulation process. The regulator cannot commit to a long-term regulatory policy, and investment decisions are taken before optimal regulatory policies are imposed. We characterize the regulated incumbent's incentive to invest when a deregulation process is initiated and an unregulated firm enters the market as a result. The change in the marginal return to investment depends on how the investment changes the firm's virtual cost—the sum of its physical production and information costs. When the marginal return to investment increases due to deregulation, social welfare increases as a result of higher investment and more competition. Otherwise, the change in social welfare depends on the total of the effects in the fall of investment and increased competition. We also present conditions under which deregulation enhances welfare.     

A theory of stopping time games with applications to product innovations and asset sales

Summary In this paper, the pure strategy subgame perfect equilibria of a general class of stopping time games are studied. It is shown that there always exists a natural class of Markov Perfect Equilibria, called stopping equilibria. Such equilibria can be computed as a solution of a single agent stopping time problem, rather than of a fixed point problem. A complete characterization of stopping equilibria is presented. Conditions are given under which the outcomes of such equilibria span the set of all possible outcomes from perfect equilibria. Two economic applications of the theory, product innovations and the timing of asset sales, are discussed.Parts of this paper were presented at seminars at Chicago, Rochester and Rutgers and we acknowledge helpful comments. We are also indebted to a referee for his detailed and thoughtful comments. The usual disclaimer applies.     

Growth,selection and appropriate contracts

We study a dynamic model where growth requires both long-term investment and the selection of talented managers. When ability is not ex-ante observable and contracts are incomplete, managerial selection imposes a cost, as managers facing the risk of being replaced choose a sub-optimally low level of long-term investment. This generates a trade-off between selection and investment that has implications for the choice of contractual relationships and institutions. Our analysis shows that rigid long-term contracts sacrificing managerial selection may prevail at early stages of economic development and when heterogeneity in ability is low. As the economy grows, however, knowledge accumulation increases the return to talent and makes it optimal to adopt flexible contractual relationships, where managerial selection is implemented even at the cost of lower investment. Measures of investor protection aimed at limiting the bargaining power of managers improve selection under short-term contracts. Given that knowledge accumulation raises the value of selection, the optimal level of investor protection increases with development.     

Aid effectiveness and limited enforceable conditionality

This paper analyzes optimal foreign aid policy in a neoclassical growth framework with a conflict of interest between the donor and the recipient government. Aid conditionality is modeled as a limited enforceable dynamic contract. We define the contract to be self-enforcing if, at any point in time, the conditions imposed on aid funds are supportable by the threat of a permanent aid cutoff from then onward. Quantitative results show that optimal self-enforcing conditional aid strongly stimulates the developing economy and substantially increases welfare. However, aid effectiveness comes at a high cost: to ensure enforceability, less benevolent political regimes receive permanently larger aid funds in return for a less intense conditionality.