Change-point models to estimate the limit of detection.

In many biological and environmental studies, measured data is subject to a limit of detection. The limit of detection is generally defined as the lowest concentration of analyte that can be differentiated from a blank sample with some certainty. Data falling below the limit of detection is left censored, falling below a level that is easily quantified by a measuring device. A great deal of interest lies in estimating the limit of detection for a particular measurement device. In this paper, we propose a change-point model to estimate the limit of detection by using data from an experiment with known analyte concentrations. Estimation of the limit of detection proceeds by a two-stage maximum likelihood method. Extensions are considered that allow for censored measurements and data from multiple experiments. A simulation study is conducted demonstrating that in some settings the change-point model provides less biased estimates of the limit of detection than conventional methods. The proposed method is then applied to data from an HIV pilot study.

Disparities in firearms ownership and storage practices in North Carolina.

OBJECTIVE: Because household firearms pose a risk to children, this study examined firearms accessibility in North Carolina households with children. METHODS: In 2008, parents completing the North Carolina Child Health Assessment and Monitoring Program survey were asked how many firearms they owned and their firearms storage practices. Weighted analyses provided estimates of ownership and storage practices and examined variation by sociodemographics. RESULTS: A total of 37% of 2885 parents reported owning firearms. Whites (adjusted odds ratio [aOR] 3.9 [95% confidence interval {CI} 2.9-5.2]), households with income >200% of the federal poverty level (aOR 1.7 [95% CI 1.2-2.5]) and married parents (aOR 2.4 [95% CI 1.8-3.4]) were more likely to own firearms. Ownership of more than one firearm was greater among whites (aOR 2.2 [95% CI 1.4-3.4]) and married parents (aOR 1.8 [95% CI 1.5-2.8]) than other groups. The number of firearms owned increased with children's age. Although most parents reported keeping firearms locked and unloaded (57%), many reported unsafe storage practices, which varied by race/ethnicity. Whites were more likely (45%) to store firearms unlocked and/or loaded than other groups (35%). CONCLUSIONS: Many North Carolina youth have access to household firearms, with white youth being more likely to have firearms, a greater number of firearms, and less safely stored firearms than other race/ethnicity groups. Further interventions and policies to reduce youth access to household firearms are needed. Future research should examine and address why whites, married couples, and those with socioeconomic advantages are more likely than individuals not belonging to these groups to own household firearms and store them unsafely.

Return of large fin whale feeding aggregations to historical whaling grounds in the Southern Ocean.

Fin whales (Balaenoptera physalus quoyi) of the Southern Hemisphere were brought to near extinction by twentieth century industrial whaling. For decades, they had all but disappeared from previously highly frequented feeding grounds in Antarctic waters. Our dedicated surveys now confirm their return to ancestral feeding grounds, gathering at the Antarctic Peninsula in large aggregations to feed. We report on the results of an abundance survey and present the first scientific documentation of large fin whale feeding aggregations at Elephant Island, Antarctica, including the first ever video documentation. We interpret high densities, re-establishment of historical behaviours and the return to ancestral feeding grounds as signs for a recovering population. Recovery of a large whale population has the potential to augment primary productivity at their feeding grounds through the effects of nutrient recycling, known as 'the whale pump'. The recovery of fin whales in that area could thus restore ecosystem functions crucial for atmospheric carbon regulation in the world's most important ocean region for the uptake of anthropogenic CO2.

Fatal and nonfatal firearm injuries in North Carolina.

This commentary discusses fatal and nonfatal injuries due to firearms in North Carolina and reviews epidemiologic trends in firearm-related homicide, suicide, and unintentional injuries. This commentary also provides an overview of strategies for reducing the risk of firearm-related injury and suggests future research to prevent these injuries.