Prevention versus Treatment under Precautionary Regulation: A Case Study of Groundwater Contamination under Uncertainty

Policy discussions on agricultural pollution problems characterize prevention as more cost effective and precautionary than ex post treatment. We derive conditions under which treatment alone is more cost effective in situations involving multiple sources of emissions, multiple sites affected, and a commonly used precautionary approach to uncertainty. We also show that a greater degree of precaution can result in less reliance on prevention. An empirical case study indicates that treatment alone is the most cost-effective means of dealing with nitrate in most Maryland community water system wells. The use of leaching prevention measures is restricted to the most intensive poultry producing areas. The incremental cost of precaution is substantial.     

Modeling Conditional Yield Densities

Given the increasing interest in agricultural risk, many have sought improved methods to characterize conditional crop-yield densities. While most have postulated the Beta as a flexible alternative to the Normal, others have chosen nonparametric methods. Unfortunately, yield data tends not to be sufficiently abundant to invalidate many reasonable parametric models. This is problematic because conclusions from economic analyses, which require estimated conditional yield densities, tend not to be invariant to the modeling assumption. We propose a semiparametric estimator that, because of its theoretical properties and our simulation results, enables one to empirically proceed with a higher degree of confidence.     

Stochastic Technology, Risk Preferences, and Adoption of Site-Specific Technologies

A model of farmer decision making is developed to determine the extent to which uncertainties about soil fertility and weather affect the value of site-specific technologies (SSTs) using jointly estimated risk and technology parameters. Uncertainty can lead risk-averse farmers to apply more fertilizers and generate more pollution than in the certainty case. Ignoring uncertainty and risk aversion would overestimate the economic and environmental benefits of SSTs and underestimate the subsidy required to induce adoption. Accounting for uncertainties and risk preferences might explain the low observed adoption rates of SSTs. Improving the accuracy of SSTs would increase the incentives for adoption.     

Estimating Willingness to Pay for Improved Water Quality in the Presence of Item Nonresponse Bias

This article deals with the problem of item nonresponse in contingent valuation surveys using a payment-card method, by applying a grouped-data sample-selection estimation technique that is capable of imputing the missing values conditional upon a respondent's decision to answer a willingness-to-pay question. The advantage of the technique lies in its ability to utilize all of the information in the sample, permitting a more efficient estimation in the presence of item nonresponse bias. The major determinants of willingness to pay appear to be household income, number of children, education, perception of existing water quality, and identification with environmental issues.     

对《形状和位置公差》新标准的理解和应用

通过对《形状和位置公差》新、旧国际的对比，综述了新、旧标准间的不同之处、便于迅速了解和应用新标准。     

Price rigidities and institutional variations in markets with posted prices

Summary Standard laboratory posted-offer markets respond slowly and incompletely to demand shocks. In these one-sided markets, where sellers control the setting of prices, very little information is transmitted via the process of exchange. For this reason, traders have trouble distinguishing randomness in their own experience from changes in market fundamentals. This paper reports the results of twelve laboratory markets conducted to assess whether some common variants to standard posted-offer rules can correct the adjustment deficiences. Although discounting, multiple postings and excess demand information all improve performance, we find that response remains poor, and efficiencies low.Support for this research was provided by the National Science Foundation (SBR 9319842 and SBR 9320044), and the University of Virginia Bankard Fund. Data are archived at FTP address: fido.econlab.arizona.edu. We wish to thank Charles Plott and Shyam Sunder for useful comments on an earlier draft of this paper. The usual disclaimer applies.     

一种新型电磁式导引器

介绍一种以负阻抗L－C振荡为基本环节的电磁式导引器，分析了其工作原理，给出了实验线路框图及位移特性。     

公共部门效率理论及实践

目前比较流行用“经济人”概念分析政府行为,但吴俊培教授在《公共部门效率理论及实践》一文中认为,把政府假设为“经济人”是不真的,在市场经济中,“经济人”是“人”的一部分,但不是全部。政府和市场一样,应该是“经济人”和“非经济人”的统一。公共部门效率不应该是纯粹经济学意义上的效率,其职责的主要目标是维持社会的公正和正义。在实践中,政府为了完成国内生产总值(GDP)的增长,甚至有招商引资的任务。这种做法不是淡化而是强化了部门利益,与公共部门的职能定位是不相符的。     

罕见的怀孕犀牛化石

9月29日,山东山旺国家地质公园古生物化石陈列馆展出一件世界罕见的长2.7米、高1.7米,怀有身孕的无角犀牛化石。这件怀胎待产的犀牛化石是在保护地质遗迹、修建硅藻土页岩剖面时发掘出土的世界上第一件完整而又怀孕的犀牛化石,距今约1800万年。上世纪七八十年代山旺山东鸟、齐鲁泰山鸟等鸟类化石的发现,填补了中新世时期的空白,从而成为国际上中新世生物建阶的重要依据,被称为“世界古生物化石宝库”。2001年末,“山旺国家自然保护区”被批准为国家地质公园后,国家先后投入2000万元对1.2平方公里的山旺国家地质公园核心区域的地质遗迹进行了…     

China’s Labor Market on Crossroad

I.IntroductionSincethelate1990s,China’slabor market has comeundergreat pressure,asreflected by anincreasing unemployment rate,and adeclining labor force participation rate.The causesofthe severe unemployment are threefold.First,due to the macro-economic downturn andrapid industrial structural change in the late1990s,state-owned enterprises(SOEs),whichlost their comparative advantage and competitiveness,have been unable to fully utilizetheir production capacity,and have become loss-makers.Se…