Statistical Issues in the Estimation of Assigned Shares for Carcinogenesis Liability

Congress is currently considering adopting a mathematical formula to assign shares in cancer causation to specific doses of radiation, for use in establishing liability and compensation awards. The proposed formula, if it were sound, would allow difficult problems in tort law and public policy to be resolved by reference to tabulated "probabilities of causation." This article examines the statistical and conceptual bases for the proposed methodology. We find that the proposed formula is incorrect as an expression for "probability and causation," that it implies hidden, debatable policy judgments in its treatment of factor interactions and uncertainties, and that it can not in general be quantified with sufficient precision to be useful. Three generic sources of statistical uncertainty are identified--sampling variability, population heterogeneity, and error propagation--that prevent accurate quantification of "assigned shares." These uncertainties arise whenever aggregate epidemiological or risk data are used to draw causal inferences about individual cases.     

Occupational stress, rescue workers and English law

This paper shows how two strands of English case law, one establishing liability to compensate for shock suffered by those at the scene of disaster, and the other concerned with physical injury suffered by rescuers, were brought together in the 1960s to provide a remedy for a rescuer suffering from what the law describes as 'nervous shock'. It further traces the development of employers' liability in this context, but finds that the law provides few examples of the contractual duty of employers to protect employees generally against stress that may cause psychological injury. It points out that there is no case law on the liability of employers for stress suffered by rescue workers, whether professional or otherwise. It notes that law reports give little guidance as to the medical evidence judges require to persuade them that nervous shock has been suffered. Finally, it spells out that EC-inspired regulations could now be used to require employers to assess, and take steps to control, stress to which their employees, including rescue workers, are exposed.     

Occupational stress,rescue workers and English law

Abstract

This paper shows how two strands of English case law, one establishing liability to compensate for shock suffered by those at the scene of disaster, and the other concerned with physical injury suffered by rescuers, were brought together in the 1960s to provide a remedy for a rescuer suffering from what the law describes as ‘nervous shock’. It further traces the development of employers' liability in this context, but finds that the law provides few examples of the contractual duty of employers to protect employees generally against stress that may cause psychological injury. It points out that there is no case law on the liability of employers for stress suffered by rescue workers, whether professional or otherwise. It notes that law reports give little guidance as to the medical evidence judges require to persuade them that nervous shock has been suffered. Finally, it spells out that EC-inspired regulations could now be used to require employers to assess, and take steps to control, stress to which their employees, including rescue workers, are exposed.     

Limiting Exposure to Collateral Liability Associated With ISO 14001 EMS Audits

The purpose of this article is to provide suggestions on how to limit the collateral liability associated with ISO 14001 environmental management system (EMS) auditing activities. Due to the detailed, invasive nature of EMS audits, companies performing such activities may expose themselves to collateral risks. Collateral risk is liability not directly associated with ISO 14001 activities, but borne through the unrelated process of EMS audit activities. Examples of collateral risks include issues of non-compliance, unintended discovery of evidence in civil tort claims and exposure to regulatory sanctions. Therefore, well-defined management of EMS audits represents an important aspect of limiting risk. This article identifies several strategies for managing and reducing these legal risks. These strategies include the rigorous management of compliance audits, concisely defining audit scopes, training auditors and auditees, understanding and using audit privileges as appropriate, exploring the use of self-declaration (for ISO 14001 conformance purposes), and using reliable document control methods. While completely eliminating liability represents a laudable but challenging goal, these methods should reduce collateral exposure to corporate and personal liability.     

The Effects of Exposure to "Synthetic" Chemicals on Human Health: A Review

This article examines how scientists use human, animal, and bacterial evidence to develop policy recommendations about the health consequences of human exposure to modern chemicals. Human evidence is limited because many epidemiological studies are contaminated with selection effects or unobserved heterogeneity. Changes in the aggregate incidence of morbidity (such as cancer) in the population over time are not a substitute for the lack of good individual-level data because incidence data are contaminated by the medicalization of cancer. Animal tests are also problematic because the expense of conducting experiments leads researchers to use only enough animals to allow detection of large differences in cancer incidence between controls and experimental animals that can only arise if the exposure doses are large. Predictions about the cancer incidence that would result in humans at much lower exposure levels, thus, require statistical inferences that implicitly make choices between false positive and false negative inference errors. Policy recommendations about carcinogens, therefore, are as much the product of value choices as "scientific" knowledge.     

产品责任预防方法与体系研究

产品责任是我国企业在加入WTO后面临的一个重要课题。由于我国在产品责任方面的立法水平较低,企业管理层尚未对产品责任问题有充分的认识。本文就造成产品责任的三种缺陷提出了产品责任预防的策略与方法。提出了将产品责任预防体系与ISO9000质量管理体系融合,达到预防产品责任,提高产品质量和企业竞争力的目的。     

Regression Versus Causation,Revisited

I recently discussed pitfalls in attempted causal inference based on reduced‐form regression models. I used as motivation a real‐world example from a paper by Dr. Sneeringer, which interpreted a reduced‐form regression analysis as implying the startling causal conclusion that “doubling of [livestock] production leads to a 7.4% increase in infant mortality.” This conclusion is based on: (A) fitting a reduced‐form regression model to aggregate (e.g., county‐level) data; and (B) (mis)interpreting a regression coefficient in this model as a causal coefficient, without performing any formal statistical tests for potential causation (such as conditional independence, Granger‐Sims, or path analysis tests). Dr. Sneeringer now adds comments that confirm and augment these deficiencies, while advocating methodological errors that, I believe, risk analysts should avoid if they want to reach logically sound, empirically valid, conclusions about cause and effect. She explains that, in addition to (A) and (B) above, she also performed other steps such as (C) manually selecting specific models and variables and (D) assuming (again, without testing) that hand‐picked surrogate variables are valid (e.g., that log‐transformed income is an adequate surrogate for poverty). In her view, these added steps imply that “critiques of A and B are not applicable” to her analysis and that therefore “a causal argument can be made” for “such a strong, robust correlation” as she believes her regression coefficient indicates. However, multiple wrongs do not create a right. Steps (C) and (D) exacerbate the problem of unjustified causal interpretation of regression coefficients, without rendering irrelevant the fact that (A) and (B) do not provide evidence of causality. This reply focuses on whether any statistical techniques can produce the silk purse of a valid causal inference from the sow's ear of a reduced‐form regression analysis of ecological data. We conclude that Dr. Sneeringer's analysis provides no valid indication that air pollution from livestock operations causes any increase in infant mortality rates. More generally, reduced‐form regression modeling of aggregate population data—no matter how it is augmented by fitting multiple models and hand‐selecting variables and transformations—is not adequate for valid causal inference about health effects caused by specific, but unmeasured, exposures.     

产品责任、企业社会责任偏好与供应链中的质量-数量协调

在产品质量和产品数量（订货量）内生化的情形下，同时实现其质量和数量的协调将成为供应链管理的一个重要问题。进一步，在产品低质量对消费者造成伤害的情形下，制造商将面临着产品责任（表征制造商对消费者产品伤害的补偿），从而导致"产品责任如何影响供应链中的质量-数量协调"这一问题。最后，如果核心企业具有对消费者的企业社会责任（CSR）偏好，则这种CSR偏好又如何影响供应链中的质量-数量协调？针对这三个问题，首先，利用批发价合同构建了一个由上游制造商和下游零售商组成的两级供应链运作博弈模型；其次考察了制造商产品责任、CSR偏好程度和质量改进效率对其产品质量决策、批发价合同和相应的供应链节点企业利润的影响；最后，研究了供应链质量-数量协调问题。结果表明：（1）产品责任不影响产品质量、订货量、供应链节点企业经济利润和消费者剩余，但制造商批发价随产品责任的增加而增加；（2）随着CSR偏好程度的增加，产品质量、订货量、零售商经济利润、供应链系统经济利润和消费者剩余随之增加，而制造商经济利润随之减小；（3）质量改进效率的提高，有利于产品质量、订货量、零售商经济利润、供应链系统经济利润和消费者剩余的增加；（4）一个由数量折扣契约和质量改进成本分担契约共同构成的协调机制，可以有效的实现供应链系统的协调，其中，产品责任将促使数量折扣契约中产品批发价的增加和质量改进成本分担比例的减小，而CSR偏好程度的增加将促使数量折扣契约中产品批发价的减小，但不影响质量改进成本分担比例。     

Estimating the Probability of Rare Events: Addressing Zero Failure Data

Traditional statistical procedures for estimating the probability of an event result in an estimate of zero when no events are realized. Alternative inferential procedures have been proposed for the situation where zero events have been realized but often these are ad hoc, relying on selecting methods dependent on the data that have been realized. Such data‐dependent inference decisions violate fundamental statistical principles, resulting in estimation procedures whose benefits are difficult to assess. In this article, we propose estimating the probability of an event occurring through minimax inference on the probability that future samples of equal size realize no more events than that in the data on which the inference is based. Although motivated by inference on rare events, the method is not restricted to zero event data and closely approximates the maximum likelihood estimate (MLE) for nonzero data. The use of the minimax procedure provides a risk adverse inferential procedure where there are no events realized. A comparison is made with the MLE and regions of the underlying probability are identified where this approach is superior. Moreover, a comparison is made with three standard approaches to supporting inference where no event data are realized, which we argue are unduly pessimistic. We show that for situations of zero events the estimator can be simply approximated with , where n is the number of trials.     

基于双层粒子群算法的上下游企业决策动态博弈

在寡占市场结构下,企业决策的相互影响效应更为显著。此时,企业融资决策与产量决策不仅仅影响自身利润,而且会影响到其竞争对手和供应商,即企业决策的策略性效应。本文建立一个考虑产品替代性与市场环境波动内外因素的上下游企业决策动态博弈模型,针对该决策的非线性二层规划特点,设计了双层粒子群算法,并利用计算机模拟技术对企业决策进行分析。研究发现,第一,产品替代性对下游企业具有“竞争效应”,对上游企业生产与利润的下降具有“放大效应”,与债务融资有限责任效应相比,产品替代性的“竞争效应”对下游企业的产量博弈和利润影响更大,另外,债务有限责任效应与债务破产效应左右了产品替代性对下游企业破产均衡临界点的影响。第二,市场环境波动对企业产量决策和融资决策的影响与Wanzenried^[1]一致,而在影响下游企业利润和上游企业利润方面并不一致。第三,针对负债融资和无负债融资两种情形,不论产品替代性较低还是较高,较高的市场波动程度都能促使负债企业考虑债务的战略性作用,且下游企业的负债融资存在“Prisoner’s Dilemma”现象,上游企业的垄断市场地位则加强了下游企业负债融资“放大效应”对其利润的影响。     

ESTIMATING EMPLOYMENT DISCRIMINATION LIABILITY WITH A DETERMINISTIC SIMULATION*

This paper presents an employment discrimination liability model that estimates back-pay liability for an employer's discriminatory employment practices by simulating employment practices under assumptions of fairness. Comparison of the racial/sexual composition of the simulated fair work force with the racial/sexual composition of the employer's actual work force permits identification of cases of discrimination. The model suggests that the choice of a stock or flow approach will have a significant effect on the amount of employer liability.     

Does Diesel Exhaust Cause Human Lung Cancer?

Recent reviews of epidemiological evidence on the relation between exposure to diesel exhaust (DE) and lung cancer risk have reached conflicting conclusions, ranging from belief that there is sufficient evidence to conclude that DE is a human lung carcinogen (California EPA, 1994) to conclusions that there is inadequate evidence to support a causal association between DE and human lung cancer (Muscat and Wynder, 1995). Individual studies also conflict, with both increases and decreases in relative risks of lung cancer mortality being cited with 95% statistical confidence. On balance, reports of elevated risk outnumber reports of reduced risk. This paper reexamines the evidence linking DE exposures to lung cancer risk. After briefly reviewing animal data and biological mechanisms, it surveys the relevant epidemiological literature and examines possible explanations for the discrepancies. These explanations emphasize the distinction between statistical associations, which have been found in many studies, and causal associations, which appear not to have been established. Methodological threats to valid causal inference are identified and new approaches for controlling them are proposed using recent techniques from artificial intelligence (AI) and computational statistics. These threats have not been adequately controlled for in previous epidemiological studies. They provide plausible noncausal explanations for the reported increases in relative risks, making it impossible to infer causality between DE exposure and lung cancer risk from these studies. A key contribution is to show how recent techniques developed in the AI-and-statistics literature can help clarify the causal interpretation of complex multivariate data sets used in epidemiological risk assessments. Applied to the key study of Garshick et al. (1988), these methods show that DE concentration has no positive causal association with occupational lung cancer mortality risk.     

Chemical Scoring by a Rapid Screening of Hazard (RASH) Method

A rapid screening of hazard method (RASH) is presented for deriving relative potency estimates for hazardous substances. The method utilizes data from any available toxicological database such as the Registry of Toxic Effects of Chemical Substances (RTECS) or EPA's GENE-TOX database on genetic activity profiles. The method has been applied to derive relative potency values and permissible environmental concentrations for 278 chemicals. The derived values have been compared with recommendations of expert committees where possible, and substantial agreement is found.     

Evaluation of Legal Liability for Technological Risks in View of Requirements for Peaceful Coexistence and Progress

Legal liability for risk‐generating technological activities is evaluated in view of requirements that are necessary for peaceful human coexistence and progress in order to show possibilities for improvement. The requirements imply, given that political decision making about the activities proceeds on the basis of majority rule, that legal liability should be unconditional (absolute, strict) and unlimited (full). We analyze actual liability in international law for various risk‐generating technological activities, to conclude that nowhere is the standard of unconditional and unlimited liability fully met. Apart from that there are enormous differences. Although significant international liability legislation is in place for some risk‐generating technological activities, legislation is virtually absent for others. We discuss fundamental possibilities and limitations of liability and private insurance to secure credible and ethically sound risk assessment and risk management practices. The limitations stem from problems of establishing a causal link between an activity and a harm; compensating irreparable harm; financial warranty; moral hazard in insurance and in organizations; and discounting future damage to present value. As our requirements call for prior agreement among all who are subjected to the risks of an activity about the settlement of these difficult problems, precautionary ex ante regulation of risk‐generating activities may be a more attractive option, either combined with liability stipulations or not. However, if ex ante regulation is not based on the consent of all subjected to the risks, it remains that the basis of liability in the law should be unconditional and unlimited liability.     

Employee stress litigation: The UK experience

This paper considers the extent to which stress-induced illness can be regarded as a personal injury that could give rise to civil action for damages against employers in the UK. It outlines the results of a brief survey of personal injury solicitors, which indicates that claims are already being initiated by employees who allege they have suffered a stress-induced illness. The potential for claims within industrial tribunal cases that have already been decided is also examined. Consideration is given to the hurdles that litigants will have to surmount, such as proving that their condition was in fact caused by some feature of their working conditions, showing that it was foreseeable that they would suffer a stress-based injury, and demonstrating that their employer was in some way at fault. This leads to a questioning of what employers can do to protect themselves from such claims, or at least defend them successfully. The paper points out that success is likely to depend heavily upon the quality of expert medical opinion, and also upon policy conditions that may influence those adjudicating on such cases. It is concluded that the cost of losing claims may be significant, and that employees who ignore the warning signs do so at their peril.     

Overcoming the liability of foreignness without strong firm capabilities — the value of market-based resources

The concept of “liability of foreignness” — the costs of doing business abroad — has been known and discussed since the mid-1970s. At the core of these discussions is the role that firm capabilities play in overcoming or limiting these costs. This raises the question of how firms with inappropriate, limited or constrained capabilities relative to their host environment overcome the liability of foreignness. This paper focuses on the subsidiaries of “emerging multinationals” and how they manage the demands of a technologically and economically highly developed host country. A host location with sophisticated markets and well-developed institutional infrastructure may be a highly challenging environment for firms that have grown their organizational capabilities in less developed contexts. This paper explores that situation and considers how resources available on the market — for example through supplier inputs — assist subsidiaries to benefit from their presence in a munificent location. Despite the acknowledged limitations of a transaction-based approach, this paper presents evidence that purchasing knowledge provides an accessible strategy for overcoming some liabilities of foreignness.     

Searching for innovation: Product,process, and business model innovations and search behavior in established firms

Prior research indicates that search practices are an important part of the innovation process. But where established firms search for different innovation types is not clear. Drawing on knowledge-based theory of innovation and using state-of-the-art statistical techniques (copula with Bayesian inference), we find that established firms predominantly rely on several external sources (broad external search) when introducing new business models, on internal and external sources with high intensity (deep search) when innovating processes, and on broad and deep external search when innovating products. We explain that broad external search is important for business model innovation (BMI) because increased exploration is needed when introducing new business models that rely on general rather than specialized technical or tacit business knowledge. We contribute to the innovation and business model literatures by nuancing the differences between innovation types (BMI, product, and process innovation) and the associated search behavior. It is important to consider these differences because they give us clues to understand how established firms can explore unfamiliar territories through BMI.     

Sample Splitting and Threshold Estimation

Threshold models have a wide variety of applications in economics. Direct applications include models of separating and multiple equilibria. Other applications include empirical sample splitting when the sample split is based on a continuously‐distributed variable such as firm size. In addition, threshold models may be used as a parsimonious strategy for nonparametric function estimation. For example, the threshold autoregressive model (TAR) is popular in the nonlinear time series literature. Threshold models also emerge as special cases of more complex statistical frameworks, such as mixture models, switching models, Markov switching models, and smooth transition threshold models. It may be important to understand the statistical properties of threshold models as a preliminary step in the development of statistical tools to handle these more complicated structures. Despite the large number of potential applications, the statistical theory of threshold estimation is undeveloped. It is known that threshold estimates are super‐consistent, but a distribution theory useful for testing and inference has yet to be provided. This paper develops a statistical theory for threshold estimation in the regression context. We allow for either cross‐section or time series observations. Least squares estimation of the regression parameters is considered. An asymptotic distribution theory for the regression estimates (the threshold and the regression slopes) is developed. It is found that the distribution of the threshold estimate is nonstandard. A method to construct asymptotic confidence intervals is developed by inverting the likelihood ratio statistic. It is shown that this yields asymptotically conservative confidence regions. Monte Carlo simulations are presented to assess the accuracy of the asymptotic approximations. The empirical relevance of the theory is illustrated through an application to the multiple equilibria growth model of Durlauf and Johnson (1995).     

Supply Chain Integration,Product Modularity,and Market Valuation: Evidence from the Solar Energy Industry

Supply chain integration is increasingly seen as a method to obtain flexibility and, consequently, to provide competitive advantage for firms within a supply chain. Product modularity, either in concert with or independent of such integration, can also produce flexibility for firms within a supply chain. In this proof‐of‐concept research, we explore whether the supply chain network affects each constituent firm's market valuation and how decisions regarding the level of supply chain integration and the usage of product modularity are associated with the value of the supply chain. We develop a method to identify and measure the supply chain's effect on each constituent firm's market valuation. Results indicate that greater integration is associated with a higher supply chain valuation, whereas increasing aggregated product modularity across the supply chain relates to a lower supply chain value. However, when combined, the interaction of aggregated product modularity and supply chain integration is positively associated with the supply chain's valuation.     

Production System Development for Expert Systems Using a Recursive Partitioning Induction Approach: An Application to Mortgage,Commercial, and Consumer Lending

The concepts of expert systems and decision support systems have received considerable attention recently. While systems have been proposed for various problem areas in business, difficulties still exist in the knowledge acquisition phase of development. This paper presents a recursive partitioning analysis (RPA) approach to knowledge acquisition. The RPA production system approach was applied to data sets representing the mortgage, commercial, and consumer lending problems. Comparison of the classification rates across these problems to the results of a generalized inductive inference production system (Quinlan's ID3 algorithm) and across the mortgage and commercial lending problems to traditional statistical modeling approaches indicated that the RPA approach provided superior results while using fewer variables.