Spatial variation in soil inorganic nitrogen across an arid urban ecosystem

We explored variations in inorganic soil nitrogen (N) concentrations across metropolitan Phoenix, Arizona, and the surrounding desert using a probability-based synoptic survey. Data were examined using spatial statistics on the entire region, as well as for the desert and urban sites separately. Concentrations of both NO₃-N and NH₄-N were markedly higher and more heterogeneous amongst urban compared to desert soils. Regional variation in soil NO₃-N concentration was best explained by latitude, land use history, population density, along with percent cover of impervious surfaces and lawn, whereas soil NH₄-N concentrations were related to only latitude and population density. Within the urban area, patterns in both soil NO₃-N and NH₄-N were best predicted by elevation, population density and type of irrigation in the surrounding neighborhood. Spatial autocorrelation of soil NO₃-N concentrations explained 49% of variation among desert sites but was absent between urban sites. We suggest that inorganic soil N concentrations are controlled by a number of ‘local’ or ‘neighborhood’ human-related drivers in the city, rather than factors related to an urban-rural gradient.     

Statistics for weighing benefits and harms in a proposed genetic substudy of a randomized cancer prevention trial

Summary.  When evaluating potential interventions for cancer prevention, it is necessary to compare benefits and harms. With new study designs, new statistical approaches may be needed to facilitate this comparison. A case in point arose in a proposed genetic substudy of a randomized trial of tamoxifen versus placebo in asymptomatic women who were at high risk for breast cancer. Although the randomized trial showed that tamoxifen substantially reduced the risk of breast cancer, the harms from tamoxifen were serious and some were life threaten-ing. In hopes of finding a subset of women with inherited risk genes who derive greater bene-fits from tamoxifen, we proposed a nested case–control study to test some trial subjects for various genes and new statistical methods to extrapolate benefits and harms to the general population. An important design question is whether or not the study should target common low penetrance genes. Our calculations show that useful results are only likely with rare high penetrance genes.     

Glass ceilings or sticky floors? A model of high-income law graduates

Minorities and females are underrepresented in the top-income quintile of law school graduates. Employing a binary logistic regression model, I examine whether this is due to a“glass ceiling” (an invisible barrier erected by third parties) or a“sticky floor” (self-imposed limitations regarding employment). My major finding is that being female, a minority, or disabled did not significantly reduce one's probability of making the top-income quintile once hours of work, experience, and other factors are taken into account. My findings directly contradict the large body of glass-ceiling literature and support the sticky-floor model. I thank the Law School Admission Council for funding this research. Helpful comments and suggestions were received from Robert Nelson of Northwestern University and the American Bar Foundation, Steven Conroy of the University of West Florida, and R. Kim Craft and Douglas Bonzo of Southern Utah University. The views expressed here are solely those of the author and do not necessarily reflect those of the institutions or persons listed above.     

An empirical Bayes' procedure for ranking players in Ryder Cup golf

We describe a model to obtain strengths and rankings of players appearing in golf's Ryder Cup. Obtaining rankings is complicated because of two reasons. First, competitors do not compete on an equal number of occasions, with some competitors appearing too infrequently for their ranking to be estimated with any degree of certainty, and second, different competitors experience different levels of volatility in results. Our approach is to assume the competitor strengths are drawn from some common distribution. For small numbers of competitors, as is the case here, we fit the model using Monte-Carlo integration. Results suggest there is very little difference between the top performing players, though Scotland's Colin Montgomerie is estimated as the strongest Ryder Cup player.     

Beyond the urban stream syndrome: organic matter budget for diagnostics and restoration of an impaired urban river

In response to water quality standard violations linked to excessive organic matter (OM) and a lack of sampling data informing the Total Maximum Daily Load (TMDL), an organic matter budget was created to quantify and identify sources of OM in the lower Jordan River (Salt Lake City, UT). By sampling dissolved, fine and coarse particulate OM, as well as measuring ecosystem metabolism at seven different sites, the researchers aimed to identify the origin of excess OM, and understand pathways by which different size classes of the OM pool are generated. The dissolved fraction (DOM; 94 %) was found to be the dominant form of OM transported within the river with fine particulate organic matter (FPOM; 6 %) the second most abundant, and coarse particulate organic matter (CPOM; 1 %) transport relatively insignificant in the overall OM budget. Primary production exceeded respiratory losses in the upper river, and this, along with OM inputs from two tributaries (where water reclamation facilities discharge into the river) delivered excess OM to the impaired lower reaches. Increasing stream metabolism index (SMI) with distance downstream (>1 in the lower river) further demonstrated that transport of excessive organic matter into the lower river was from upstream sources and not due to lateral inputs. This simple approach to characterizing the organic matter budget as it relates to water quality in the Jordan River was effective and could serve as a model for future studies attempting to quantify and identify sources of OM in urban ecosystems.     

Childless Elders in Assisted Living: Findings from the Maryland Assisted Living Study

We compared data drawn from a random sample of 399 current assisted living residents and a subsample of 222 newly admitted residents for two groups: childless residents and residents with children. The percentage of childless residents (26%) in our study was slightly higher than U.S. population estimates of childless individuals aged 65 years and older (20%). In the overall sample, the two groups differed significantly by age, race, and women's years of education. The childless group was slightly younger, had a higher percentage of African American residents, and had more years of education than the group with children. In the subsample, we looked at demographic, functional, financial, and social characteristics and found that childless residents reported fewer diagnoses of dementia and fewer visits from a relative but more reported paying less money per month for assisted living and having private insurance than residents with children. As childlessness among older adults continues to increase, it will become increasingly important to understand how child status affects the need for and experience of long-term care.     

Characteristics of children in residential treatment in New York State

This study addresses three questions about the population of children and families served in the highest level of care in the child welfare system in New York State residential treatment centers (RTCs): (1) How prevalent are emotional and behavioral problems in the youth entering RTCs? (2) Has the proportion of youth with such problems increased compared to 10 years ago? (3) Are there identifiable subgroups of youth entering RTCs? One-fourth of RTC admissions in fiscal year 2001 were randomly selected from a representative sample of 16 RTCs. The study completed a standardized data collection instrument based on a review of agency records, and included information that was known at the time each child was admitted. The results show significant increases compared to t10 years earlier in the proportion of youth with mental health problems and juvenile justice backgrounds. The findings suggest that youth who traditionally have been served by other systems of care are now being served in the child welfare system. The increased treatment needs of these youth and the heterogeneity of the RTC population have important implications for policies, programs, and practice.     

Maintenance of skilled performance with age: a descriptive examination of professional golfers

Demographic studies indicate a remarkable aging trend in North America. An accurate profile of the decline in physical and cognitive capabilities over time is essential to our understanding of the aging process. This study examined the maintenance of skilled performance across the careers of 96 professional golfers. Data were collected on scoring average, driving distance, driving accuracy, greens in regulation, putts per round, and number of competitive rounds played using online data archives. Analyses indicate that performance in this activity can be maintained to a greater extent than in activities relying on biologically constrained abilities. Although the generalizability of these results to "normal" aging populations is not known, they suggest that acquired skills can be maintained to a large extent in the face of advancing age.