A Deliberative Method for Ranking Risks (II): Evaluation of Validity and Agreement among Risk Managers

A deliberative method for ranking risks was evaluated in a study involving 218 risk managers. Both holistic and multiattribute procedures were used to assess individual and group rankings of health and safety risks facing students at a fictitious middle school. Consistency between the rankings that emerged from these two procedures was reasonably high for individuals and for groups, suggesting that these procedures capture an underlying construct of riskiness. Participants reported high levels of satisfaction with their groups' decision-making processes and the resulting rankings, and these reports were corroborated by regression analyses. Risk rankings were similar across individuals and groups, even though individuals and groups did not always agree on the relative importance of risk attributes. Lower consistency between the risk rankings from the holistic and multiattribute procedures and lower agreement among individuals and groups regarding these rankings were observed for a set of high-variance risks. Nonetheless, the generally high levels of consistency, satisfaction, and agreement suggest that this deliberative method is capable of producing risk rankings that can serve as informative inputs to public risk-management decision making.     

Modelling cell generation times by using the tempered stable distribution

Summary.  We show that the family of tempered stable distributions has considerable potential for modelling cell generation time data. Several real examples illustrate how these distributions can improve on currently assumed models, including the gamma and inverse Gaussian distributions which arise as special cases. Our applications concentrate on the generation times of oligodendrocyte progenitor cells and the yeast Saccharomyces cerevisiae . Numerical inversion of the Laplace transform of the probability density function provides fast and accurate approximations to the tempered stable density, for which no closed form generally exists. We also show how the asymptotic population growth rate is easily calculated under a tempered stable model.     

Explosion Probability of Unexploded Ordnance: Expert Beliefs

This article reports on a study to quantify expert beliefs about the explosion probability of unexploded ordnance (UXO). Some 1,976 sites at closed military bases in the United States are contaminated with UXO and are slated for cleanup, at an estimated cost of $15–140 billion. Because no available technology can guarantee 100% removal of UXO, information about explosion probability is needed to assess the residual risks of civilian reuse of closed military bases and to make decisions about how much to invest in cleanup. This study elicited probability distributions for the chance of UXO explosion from 25 experts in explosive ordnance disposal, all of whom have had field experience in UXO identification and deactivation. The study considered six different scenarios: three different types of UXO handled in two different ways (one involving children and the other involving construction workers). We also asked the experts to rank by sensitivity to explosion 20 different kinds of UXO found at a case study site at Fort Ord, California. We found that the experts do not agree about the probability of UXO explosion, with significant differences among experts in their mean estimates of explosion probabilities and in the amount of uncertainty that they express in their estimates. In three of the six scenarios, the divergence was so great that the average of all the expert probability distributions was statistically indistinguishable from a uniform (0, 1) distribution—suggesting that the sum of expert opinion provides no information at all about the explosion risk. The experts' opinions on the relative sensitivity to explosion of the 20 UXO items also diverged. The average correlation between rankings of any pair of experts was 0.41, which, statistically, is barely significant (p= 0.049) at the 95% confidence level. Thus, one expert's rankings provide little predictive information about another's rankings. The lack of consensus among experts suggests that empirical studies are needed to better understand the explosion risks of UXO.     

Insurance decisions for low-probability losses

It is widely accepted that individuals tend to underinsure against low-probability, high-loss events relative to high-probability, low-loss events. This conventional wisdom is based largely on field studies, as there is very little experimental evidence. We reexamine this issue with an experiment that accounts for possible confounds in prior insurance experiments. Our results are counter to the prior experimental evidence, as we observe subjects buying more insurance for lower-probability events than for higher-probability events, given a constant expected loss and load factor. Insofar as underinsurance for catastrophic risk is observed in the field, our results suggest that this can be attributed to factors other than only the relative probability of the loss events.

Missing data: Discussion points from the PSI missing data expert group

The Points to Consider Document on Missing Data was adopted by the Committee of Health and Medicinal Products (CHMP) in December 2001. In September 2007 the CHMP issued a recommendation to review the document, with particular emphasis on summarizing and critically appraising the pattern of drop‐outs, explaining the role and limitations of the ‘last observation carried forward’ method and describing the CHMP's cautionary stance on the use of mixed models. In preparation for the release of the updated guidance document, statisticians in the Pharmaceutical Industry held a one‐day expert group meeting in September 2008. Topics that were debated included minimizing the extent of missing data and understanding the missing data mechanism, defining the principles for handling missing data and understanding the assumptions underlying different analysis methods. A clear message from the meeting was that at present, biostatisticians tend only to react to missing data. Limited pro‐active planning is undertaken when designing clinical trials. Missing data mechanisms for a trial need to be considered during the planning phase and the impact on the objectives assessed. Another area for improvement is in the understanding of the pattern of missing data observed during a trial and thus the missing data mechanism via the plotting of data; for example, use of Kaplan–Meier curves looking at time to withdrawal. Copyright © 2009 John Wiley & Sons, Ltd.     

Factors That Influence Willingness to Help the Homeless

Homelessness is an ongoing challenge for many families and individuals. Many struggle to meet their basic needs for food, clothing and shelter. Unfortunately, we know very little about the people who directly help homeless people meet these needs. The present study examines the relationships between empathy, religion, household income, political orientation, gender, race, and people's expressed willingness to assist the homeless. Results demonstrate a strong and consistent link between empathy and willingness to help. Moderately consistent associations are found for religion and race. Limitations, suggestions for further research, and for practical application are discussed.     

The myth of labor’s inequality of bargaining power

This paper argues that the widespread belief in labor’s exploitation and “underpayment” in a free market economy is illogical and lacks a serious empirical foundation. Theories of systematic disadvantage ignore the behavior of entrepreneurs under the profit-and-loss motive and the tendency for risk-adjusted rates of return to equalize. Labor has proven versatile and mobile in the U.S. economy, where technical progress also has been extraordinarily labor-saving. Nor have discrimination (when unaided by the public sector), fluctuations in unemployment, or formal collusions resulted in systematic underpricing of labor services. The author thanks John Allen and Donald Deere for their comments on an earlier draft of this paper. The usual caveat holds.     

Contextual Factors in the Rise of Academic Sociology in the United States*

Cet article effectue l'analyse de certains elements culturels et educatifs qui favoriserent la croissance de la sociologie en tant que discipline universitaire aux Etats-Unis a la fin du dix-neuvieme siecle. II est a remarquer que cette evolution est unique au contexte americain. Les facteurs qui retiennent l'at-tention de l'auteur son les suivants: les attitudes vis-a-vis l'education superieure; rinfluence des ideaux et methodes allemands concernant l'education; la con-fiance que Ton avait dans la valeur de la science, y compris les sciences sociales; le climat ideologique liberal de la societe americaine et, par voie de consequence, des universites; et l'etat d'avancement de la theorie sociologique aux Etats-Unis durant cette periode. This paper is concerned with some of the cultural and educational elements in late nineteenth-century America which allowed for and fostered the ready growth of sociology as a university discipline at that time, a growth not to be found in other countries. Specific factors investigated are the attitude towards higher education, the influence of German ideals and methods on that education, the belief in the value of science, including social science, the liberal ideological climate of the society and hence of the universities, and the general state of sociological theory in the United States in this period.     

Two measures of geographic location and their relation to income

Two different ways of categorizing people’s geographical location are compared as to their relation to earned incomes of family heads, after adjustment for education, age, sex and race. One, the traditional code, uses the size of the city in which the family lives. The other, originally suggested by Bernard Lazerwitz, focuses on the distance to, and the size of, the central city of the nearest standard metropolitan statistical area. Both appear useful, and their joint effects are examined.