Modeling Cholinesterase Activity for Human Dietary Risk Assessment of Carbamate Insecticides

This article demonstrates statistical models to quantify the interaction between a carbamate insecticide and acetylcholinesterase. Carbamates are a class of chemicals that inhibit the activity of acetylcholinesterase in humans, an enzyme involved in the regulation of the neurotransmitter acetylcholine. Following exposure to a carbamate insecticide, we specifically address (1) if acetylcholinesterase activity recovers to its level of preexposure activity; (2) the level of inhibition of acetylcholinesterase activity; (3) the recovery time of acetylcholinesterase activity to its preexposure level for a typical individual; and (4) the upper percentiles of the recovery time of acetycholinesterase activity across individuals. A nonlinear mixed-effects model is fitted to data from a repeated measures experiment conducted with human volunteers randomly assigned to a control and four dose groups. Repeated measurements were taken prior to exposure and at 1, 2, 4, 6, 8, and 21 hours after exposure to the carbamate aldicarb. It was found that full recovery did occur. Inhibition at 1 hour was estimated with maximum inhibition most likely occurring prior to 1-hour postexposure. In addition, recovery was rapid even for sensitive individuals. Given this information, the potential effect from exposure to a carbamate consumed in the diet during a day can be quantitatively assessed.     

A Caution on Comparisons

Abstract

The family is the foundation of our society. By learning about family life in other countries, we learn about our own lives and we realize that we all belong to one big family—the family of mankind. … [Studying families of the world] could help us to get closer to people in distant countries and support the knowledge that “we are one.” — Liv Ullmann, UNICEF Goodwill Ambassador     

Reanalysis of Dose-Response Data from the Iraqi Methylmercury Poisoning Episode

Applying a hockey stick parametric dose-response model to data on late or retarded development in Iraqi children exposed in utero to methylmercury, with mercury (Hg) exposure characterized by the peak Hg concentration in mothers'hair during pregnancy, Cox et al. calculated the "best statistical estimate" of the threshold for health effects as 10 ppm Hg in hair with a 95% range of uncertainty of between 0 and 13.6 ppm.⁽¹⁾A new application of the hockey stick model to the Iraqi data shows, however, that the statistical upper limit of the threshold based on the hockey stick model could be as high as 255 ppm. Furthermore, the maximum likelihood estimate of the threshold using a different parametric model is virtually zero. These and other analyses demonstrate that threshold estimates based on parametric models exhibit high statistical variability and model dependency, and are highly sensitive to the precise definition of an abnormal response. Consequently, they are not a reliable basis for setting a reference dose (RfD) for methylmercury. Benchmark analyses and statistical analyses useful for deriving NOAELs are also presented. We believe these latter analyses—particularly the benchmark analyses—generally form a sounder basis for determining RfDs than the type of hockey stick analysis presented by Cox et al. However, the acute nature of the exposures, as well as other limitations in the Iraqi data suggest that other data may be more appropriate for determining acceptable human exposures to methylmercury.     

Nonresponse in the American Time Use Survey: Who Is Missing from the Data and How Much Does It Matter?

This article examines nonresponse in a large government survey,the American Time Use Survey (ATUS), which interviews personsin households previously interviewed in the Current PopulationSurvey. The response rate for the ATUS has been below 60 percentfor the first two years of its existence, raising questionsabout whether the results can be generalized to the target population.The article begins with an analysis of the types of nonresponseencountered in the ATUS. Noncontact accounts for roughly 60percent of ATUS nonresponse, with refusals accounting for roughly40 percent. We find little support for the hypothesis that busypeople are less likely to respond to the ATUS but find considerablesupport for the hypothesis that people who are weakly integratedinto their communities are less likely to respond, mostly becausethey are less likely to be contacted. When we compare aggregateestimates of time use calculated using the ATUS base weightswithout any adjustment for nonresponse, estimates calculatedusing the ATUS final weights with a nonresponse adjustment,and estimates calculated using weights that incorporate ourown nonresponse adjustment based on a propensity model, we findsome modest differences, but the three sets of estimates arebroadly similar. The article ends with suggestions for furtherresearch and analysis.     

‘Germany Has Become Mohammedan’: Insurgency,Long-Distance Travel,and the Singapore Mutiny, 1915

Abstract

The mutiny that took place in Singapore in February 1915 is usually dismissed as a footnote in the history of empire. One reason why it is marginalized is because the mutiny does not conform to a politics that seeks the formation of an independent territorial nation-state as its inevitable conclusion. This article returns to that initial moment of insurgency to argue that the mutiny offers a unique window into the political imaginaries of British Indian soldiers, seen as military migrant workers. A close reading of soldiers’ letters against the Rowlatt Committee's Sedition Report suggests a politics of equality and emancipation uncontaminated by the desire for national liberation. Two kinds of insurgency thus become visible: international space as an unsettled zone of attraction and desire and a nascent political subjectivity that rejects the disciplines of imperial military labor. The primary causes of these transformations, I argue, are the insurgent effects of long-distance travel.     

Unsupervised Curve Clustering using B-Splines

Data in many different fields come to practitioners through a process naturally described as functional. Although data are gathered as finite vector and may contain measurement errors, the functional form have to be taken into account. We propose a clustering procedure of such data emphasizing the functional nature of the objects. The new clustering method consists of two stages: fitting the functional data by B‐splines and partitioning the estimated model coefficients using a k‐means algorithm. Strong consistency of the clustering method is proved and a real‐world example from food industry is given.     

Leader–member exchange,feelings of energy,and involvement in creative work

This study examined how leaders create the impetus for creativity at work. One hundred ninety-three employees occupying a variety of jobs in Israeli organizations completed surveys at two points in time to assess their perceptions of the quality of their relationship with their leader (LMX), their level of energy, and their creative work involvement. SEM and regression analyses showed that LMX was positively related to employees' feelings of energy, which in turn were related to a high level of involvement in creative work. Factors that leaders should take into consideration in promoting followers' creative behaviors are discussed.     

Limit Distributions of Random Sums of Z+-Valued Random Variables

In this article, we formulate a transfer theorem in terms of probability generating functions and discuss two approaches to limit distributions of random sums of Z ₊-valued random variables. We then develop Z ₊-valued N-ID and ?-ID laws.