The role of variations in growth rate and sample collection on interpreting results of segmental analyses of hair

Segmental analysis of hair for drugs, metabolites, and poisons has been widely reported in the scientific literature over the past two decades. Two fundamental assumptions in interpreting results of such analyses are (1) an average linear growth rate of head hair of 1cm/month and (2) that sample collections occur with the hair being cut directly next to the scalp. The purpose of this study was to evaluate the variability associated with growth rate of human head hair, as well as the ability to uniformly collect hair next to the scalp. The results were used to determine how these factors affect the interpretation of results generated in segmental analysis of hair. A thorough literature review was conducted to assess the range of linear growth of human head hair from the vertex posterior and occipital regions. The results were compiled to establish the average (1.06cm/month), as well as the range of possible growth rates of head hair. The range was remarkable and suggests that conclusions based on the 1-cm/month growth rate could be significantly skewed. A separate study was undertaken to evaluate collection of hair next to the scalp. Fourteen individuals were provided oral instructions, as well as a written standard collection procedure for head hair. The experience levels among the collectors varied from novice to expert. Each individual collected hair from dolls with short- and long-hair. Immediately following each collection, the sampling area was evaluated to determine how close to the scalp the cuts were made, as well as the variability in the lengths of hair remaining at the sampled area. From our collection study, we determined that 0.8±0.1cm of hair was left on the scalp after cutting. When taking into account the amount of hair left on the scalp after collecting, the use of a growth rate of 1.06cm/month, and the assumption that it takes two weeks for newly formed hair in the follicle to reach the scalp, we find that the first 1-cm segment of hair typically corresponds to hair formed 1.3±0.2 to 2.2±0.4 months (95% confidence) earlier. The impact of these findings as it relates to the corresponding time for each additional segment is demonstrated. As a result, we recommend that hair collection be delayed 8 weeks after a suspected ingestion to ensure that the sample fully represents the exposure period. The results of this study suggest that the variability in the growth rate of human head hair, as well as the inconsistent collection of hair, significantly affect the interpretation of results from segmental analysis of hair.     

Yes we can! Valence politics and electoral choice in America, 2008

The claim that the 2008 presidential election was a transformative one is fast becoming part of the conventional wisdom of American politics. Despite the election’s undoubted significance, this paper argues that factors affecting voting decisions were strikingly similar to those operating in many previous presidential elections. Using data from the CCAP six-wave national election survey, we demonstrate that a valence politics model provides a powerful, parsimonious explanation of the ballot decisions Americans made in 2008. As is typical in presidential elections, candidate images had major effects on electoral choice. Controlling for several other relevant factors, racial attitudes were strongly associated with how voters reacted to the candidates. Other models of electoral choice, such as a Downsian issue-proximity model, are also relevant, but their explanatory power is considerably less than that provided by the valence politics model.     

African American adolescents living and coping with community violence on Chicago's southside

This study explores community violence exposures among African American adolescents and whether coping strategies were gendered. In-depth interviews are conducted with a sample of 32 African American high school students. Data are analyzed using a thematic analysis. The primary forms of violence exposures are physical attacks, fighting, and incidents involving police, gun violence, and murders. Boys report more exposure to violence as victims and witnesses, whereas girls are more likely to hear about violent acts. Coping styles range from "getting through," which included both an acceptance of community conditions; "getting along," which included self-defense techniques; "getting away," which included avoidance coping strategies; and "getting back," which consisted of confrontational coping strategies. Boys report more confrontational coping styles than are girls, who utilized more avoidance approaches. Widespread school-based interventions are warranted, given the high prevalence of community violence exposure among these youth and may provide important supports for coping against such trauma.