Steven J. Schwager

A comparison of association indices

Abstract Indices used to measure the frequency of association between individuals in fission/fusion societies are frequently borrowed from ecological studies of species association without adequate justification. In this paper several such indices, under specific conditions likely to be encountered in field studies of animal behaviour, are examined. Each of three indices commonly found in the literature is shown through simulations to be accurate over only a narrow range of possible sampling biases. As an alternative approach, examples are given of the derivation of a maximum-likelihood estimator based on two simple models. Both models assume that a constant proportion of existing subgroups is located. In the first model all combinations of subgroups are equally likely to be located, while in the second model the probability of locating one subgroup is allowed to differ from that of the others. The maximum-likelihood estimators are shown to be less biased and to have lower variance than the other three indices under the assumptions of the models.

An Information Interpretation of Financial Analyst Superiority in Forecasting Earnings

This paper develops and tests an information-based model for conditions under which analysts earnings forecasts are likely to be more accurate than forecasts of time-series models. Three information variables are considered, namely the dimensionality of the information set, the precision of the information items, and the correlation amongst the information items. The respective proxy variables for the information variables are firm size, extent of agreement amongst analysts, and the number of lines of business the firm operates in. Evidence is provided that analysts are likely to be more accurate than time series models for larger firms and for firms whereby analysts have more homogeneous earnings forecasts.

Risk-based consumption advice for farmed Atlantic and wild Pacific salmon contaminated with dioxins and dioxin-like compounds

We reported recently that several organic contaminants occurred at elevated concentrations in farmed Atlantic salmon compared with concentrations of the same contaminants in wild Pacific salmon [Hites et al. Science 303:226–229 (2004)]. We also found that polychlorinated biphenyls (PCBs), toxaphene, dieldrin, dioxins, and polybrominated diphenyl ethers occurred at higher concentrations in European farm-raised salmon than in farmed salmon from North and South America. Health risks (based on a quantitative cancer risk assessment) associated with consumption of farmed salmon contaminated with PCBs, toxaphene, and dieldrin were higher than risks associated with exposure to the same contaminants in wild salmon. Here we present information on cancer and noncancer health risks of exposure to dioxins in farmed and wild salmon. The analysis is based on a tolerable intake level for dioxin-like compounds established by the World Health Organization and on risk estimates for human exposure to dioxins developed by the U.S. Environmental Protection Agency. Consumption of farmed salmon at relatively low frequencies results in elevated exposure to dioxins and dioxin-like compounds with commensurate elevation in estimates of health risk.

Run Probabilities in Sequences of Markov-Dependent Trials

Abstract The probability of the occurrence of a run R is obtained as a function of the composition of R, the number n of trials, and the probabilities of the v ≥ 2 possible outcomes at each trial. The run R can consist of any specified sequence of outcomes, and the probability that one or more of a given collection of runs occurs is also evaluated. The probabilities of the v possible outcomes can vary arbitrarily from trial to trial, and can be L-order Markov dependent on the L preceding outcomes. The practical application of these results is discussed.

A survey of metals in tissues of farmed Atlantic and wild Pacific salmon

Contamination of fish tissues with organic and inorganic contaminants has been a pervasive environmental and public health problem. The present study reports the concentrations of nine metals in tissues of farmed Atlantic salmon (Salmo salar) and two species of wild-caught salmon (chum [Oncorhynchus keta] and coho [O. kisutch]) analyzed as part of a global survey of contaminants in these fish. Of the nine metals, organic arsenic was significantly higher in farmed than in wild salmon, whereas cobalt, copper, and cadmium were significantly higher in wild salmon. None of the contaminants exceeded federal standards or guidance levels.

Mapping of ripening-related or -specific cDNA clones of tomato (Lycopersicon esculentum)

SummaryNineteen ripening-related or -specific clones from Lycopersicon esculentum were mapped via RFLP analysis using an F2 population from the cross L. esculentum x L. pennellii and cDNA or genomic clones of known map location. The map produced using cDNA and genomic clones of known map location corresponded well with previously published maps of tomato. The number of loci detected for each ripening-related or-specific clone varied from one to seven. These loci were located on all 12 chromosomes of the tomato genome. There was no significant clustering of ripening-related or-specific genes. Regions of very low recombination were observed. The clone for polygalacturonase (TOM6) mapped to a single region on chromosome 10, the same chromosome as the nor and alc ripening mutants. To fine map this chromosome, two backcross populations were produced from the cross of L. esculentum x L. pimpenillifolium, in which the esculentum parents used were homozygous for either the alc or the nor. The coding region for polygalacturonase is functionally unlinked to either of these two ripening mutants.

Improved cell sensitivity and longevity in a rapid impedance-based toxicity sensor.

A number of toxicity sensors for testing field water using a range of eukaryotic cell types have been proposed, but it has been difficult to identify sensors with both appropriate sensitivity to toxicants and the potential for long‐term viability. Assessment of bovine pulmonary artery endothelial cell (BPAEC) monolayer electrical impedance with electric cell‐substrate impedance sensing (ECIS) showed promise in a previous systematic evaluation of toxicity sensor technologies. The goal of the study reported here was to improve toxicant responsiveness and field portability of this cell‐based toxicity sensor. A variety of human cells, non‐human mammalian cells, and non‐mammalian vertebrate cells were screened for sensitivity to 12 waterborne industrial chemicals. The results of this assessment show that bovine lung microvessel endothelial cell (BLMVEC) monolayers and iguana heart (IgH‐2) cell monolayers could detect nine out of the 12 waterborne industrial chemicals, an improvement over the seven chemicals previously detected using BPAEC monolayers. Both the BLMVEC and IgH‐2 cell monolayers were tested for their ability for long‐term survival on the ECIS test chips in a laboratory environment. Both cell lines were able to maintain high impedance readings on the ECIS electrodes for 37 days, a key trait in developing a field‐portable toxicity sensor for water. Cell line optimization has greatly contributed to the on‐going development of a field‐portable cell‐based biosensor that detects with sensitivity a wide range of waterborne toxicants. Published in 2009 by John Wiley & Sons, Ltd.

ESTIMATING VARIABILITY IN SOIL ORGANIC CARBON STORAGE USING THE METHOD OF STATISTICAL DIFFERENTIALS

The diverse nature of soils introduces uncertainty into the estimation of soil organic carbon (SOC) storage. Laboratory analyses indicate C concentration in soils, but the soil layer thickness, bulk density, and percent of fragments > 2 mm must be known in order to estimate SOC storage. Ideally, measurements of SOC concentration are performed on the same soil samples used to determine bulk density and percent of fragments > 2 mm, but this is frequently not possible. Often measurements of SOC concentration, bulk density, and percent of fragments > 2 mm are obtained separately from the same soil layer, which causes propagation of error when estimating SOC storage. Furthermore, measurements of bulk density and percent of fragments > 2 mm are more difficult to obtain than measurements of SOC concentration. Because of this, samples of bulk density and percent of fragments > 2 mm are often taken independently and less frequently than samples for SOC concentration. The objective of this study was to derive an estimation method for the variability in SOC storage estimates as a function of SOC concentration, bulk density, percent of fragments > 2 mm, and soil thickness. The method of statistical differentials, also known as the delta method, was used to obtain an estimate of the variability in SOC storage estimates. The variance estimation procedure is illustrated using previously published data for the Russian Chernozem under different management regimes. The method of statistical differentials is a valuable tool for obtaining variance estimates in a large class of problems with similar characteristics.

Lessons from Nigeria : the role of roads in the geo-temporal progression of avian influenza (H5N1) virus

The daily progression of the 2006 (January-June) Nigerian avian influenza (AI H5N1) epidemic was assessed in relation to both spatial variables and the generation interval of the invading virus. Proximity to the highway network appeared to promote epidemic dispersal: from the first AI generation interval onwards > 20% of all cases were located at < 5 km from the nearest major road. Fifty-seven per cent of all cases were located 31 km from three highway intersections. Findings suggest that the spatial features of emerging infections could be key in their control. When the spatial location of a transmission factor is well known, such as that of the highway network, and a substantial percentage of cases (e.g. > 20%) are near that factor, early interventions focusing on transmission factors, such as road blocks that prevent poultry trade, may be more efficacious than interventions applied only to the susceptible population.

Bonferroni Sometimes Loses

Abstract Bonferroni inequalities often provide tight upper and lower bounds for the probability of a union of events. The bounds are especially useful when this probability is difficult to compute exactly. There are situations, however, in which the Bonferroni approach gives very poor results. An example is given in which the upper and lower Bonferroni bounds are far from the probability they seek to approximate and successive bounds do not converge. Even an improved first upper Bonferroni bound may not be close to the probability of the union of events.