Sample Size and Robustness of Inferences from Logistic Regression in the Presence of Nonlinearity and Multicollinearity

The logistic regression models has been widely used in the social and natural sciences and results from studies using this model can have significant impact. Thus, confidence in the reliability of inferences drawn from these models is essential. The robustness of such inferences is dependent on sample size. The purpose of this study is to examine the impact of sample size on the mean estimated bias and efficiency of parameter estimation and inference for the logistic regression model. A number of simulations are conducted examining the impact of sample size, nonlinear predictors, and multicollinearity on substantive inferences (e.g. odds ratios, marginal effects) and goodness of fit (e.g. pseudo-R2, predictability) of logistic regression models. Findings suggest that sample size can affect parameter estimates and inferences in the presence of multicollinearity and nonlinear predictor functions, but marginal effects estimates are relatively robust to sample size.Logistic Regression Model, Multicollinearity, Nonlinearity, Robustness, Small Sample Bias, Research Methods/ Statistical Methods,

Farm Efficiency and Productivity Growth: The Effect of Commodity Prices

Crop prices can affect farm productivity through input- output decisions. This study assesses the relationship between crop prices and productivity changes among a sample of Kansas farms. The changes in total factor productivity are evaluated using a nonparametric approach with a Malmquist productivity index and potential drivers of technical efficiency and productivity change are analyzed. Farms with higher leverage and greater diversification are likely to be more efficient and experience productivity change. Lower productivity occurred during years with higher crop prices, suggesting that innovation is more likely to occur when margins are tight

“I don’t want to look sick skinny”: Perceptions of body image and weight loss in Hispanics living with HIV in South Texas

Objective: Obesity is rising in people with HIV (PLWH) and Hispanics. Both HIV and obesity are associated with cardiovascular disease morbidity and mortality. Our goal is to understand perceptions of body image and lifestyle in Hispanics with HIV to adapt interventions appropriately. Methods: We conducted semi-structured interviews with 22 Hispanic PLWH and 6 providers. Purposive sampling selected patient participants across weights and genders. Interviews were coded and analyzed using grounded theory, comparing perspectives between patients with and without obesity, and patients and providers. Results: Participants felt obesity and diabetes were “normal” in the community. Patients exhibited understanding of healthy diet and lifestyle but felt incapable of maintaining either. Traditionally Hispanic foods were blamed for local obesity prevalence. Five patients equated weight with health and weight loss with illness, and four expressed concerns that weight loss could lead to unintentional disclosure of HIV status. Participants with overweight or obesity expressed awareness of their weight and felt shamed by providers. Providers found weight loss interventions to be ineffective. Conclusion: Interventions in this population must address identified barriers: overweight/obesity as a normative value, lack of self-efficacy, cultural beliefs surrounding food, fear of HIV-associated weight loss and stigma, and provider perspectives on intervention futility

A Delphi Study on Research Priorities for Trauma Nursing

Objectives: To identify and prioritize research questions of importance to trauma patient care and of interest to trauma nurses. Methods: A three-round Delphi technique was used to solicit, identify, and prioritize problems for trauma nursing research. In round 1, experienced trauma nurses (N = 208) generated 513 problems, which were analyzed, categorized, and collapsed into 111 items for subsequent rounds. Round 2 participants rated each research question on a 1 to 7 scale on two criteria: impact on patient welfare and value for practicing nurses. Group median scores provided by 166 round 2 respondents and respondents\u27 individual round 2 scores were indicated on the round 3 questionnaire. Subjects rated the questions again on the same criteria and indicated whether nurses, independently or in collaboration with other health professionals, should assume responsibility for that research. Median and mean scores and rank order were determined for each item. Results: Respondents who completed all three rounds (n = 137) had a mean of 8.3 years of trauma experience. Nine research questions ranked within the top 20 on both criteria. The two research questions that ranked highest on both criteria were: What are the most effective nursing interventions in the prevention of pulmonary and circulatory complications in trauma patients? and What are the most effective methods for preventing aspiration in trauma patients during the postoperative phase? The third-ranked question regarding patient welfare was: What psychological and lifestyle changes result from traumatic injury? Regarding value for practicing nurses, What are the most effective educational methods to prepare and maintain proficiency in trauma care providers? ranked third. Conclusion: These research priorities provide impetus and direction for nursing and collaborative investigation in trauma care

Starvation Resistance is Associated with Developmentally Specified Changes in Sleep, Feeding and Metabolic Rate

Food shortage represents a primary challenge to survival, and animals have adapted diverse developmental, physiological and behavioral strategies to survive when food becomes unavailable. Starvation resistance is strongly influenced by ecological and evolutionary history, yet the genetic basis for the evolution of starvation resistance remains poorly understood. The fruit fly Drosophila melanogaster provides a powerful model for leveraging experimental evolution to investigate traits associated with starvation resistance. While control populations only live a few days without food, selection for starvation resistance results in populations that can survive weeks. We have previously shown that selection for starvation resistance results in increased sleep and reduced feeding in adult flies. Here, we investigate the ontogeny of starvation resistance-associated behavioral and metabolic phenotypes in these experimentally selected flies. We found that selection for starvation resistance resulted in delayed development and a reduction in metabolic rate in larvae that persisted into adulthood, suggesting that these traits may allow for the accumulation of energy stores and an increase in body size within these selected populations. In addition, we found that larval sleep was largely unaffected by starvation selection and that feeding increased during the late larval stages, suggesting that experimental evolution for starvation resistance produces developmentally specified changes in behavioral regulation. Together, these findings reveal a critical role for development in the evolution of starvation resistance and indicate that selection can selectively influence behavior during defined developmental time points

Bostonia: v. 63, no. 3

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Overview of C/C-SiC Composite Development for the Orion Launch Abort System

Past and present efforts by the authors to further understanding of the ceramic matrix composite (CMC) material used in the valve components of the Orion Launch Abort System (LAS) Attitude Control Motor (ACM) will be presented. The LAS is designed to quickly lift the Orion Crew Exploration Vehicle (CEV) away from its launch vehicle in emergency abort scenarios. The ACM is a solid rocket motor which utilizes eight throttleable nozzles to maintain proper orientation of the CEV during abort operations. Launch abort systems have not been available for use by NASA on manned launches since the last Apollo ]Saturn launch in 1975. The CMC material, carbon-carbon/silicon-carbide (C/C-SiC), is manufactured by Fiber Materials, Inc. and consists of a rigid 4-directional carbon-fiber tow weave reinforced with a mixed carbon plus SiC matrix. Several valve and full system (8-valve) static motor tests have been conducted by the motor vendor. The culmination of these tests was the successful flight test of the Orion LAS Pad Abort One (PA ]1) vehicle on May 6, 2010. Due to the fast pace of the LAS development program, NASA Marshall Space Flight Center assisted the LAS community by performing a series of material and component evaluations using fired hardware from valve and full ]system development motor tests, and from the PA-1 flight ACM motor. Information will be presented on the structure of the C/C-SiC material, as well as the efficacy of various non ]destructive evaluation (NDE) techniques, including but not limited to: radiography, computed tomography, nanofocus computed tomography, and X-ray transmission microscopy. Examinations of the microstructure of the material via scanning electron microscopy and energy dispersive spectroscopy will also be discussed. The findings resulting from the subject effort are assisting the LAS Project in risk assessments and in possible modifications to the final ACM operational design

Regional variability of diatoms in ice cores from the Antarctic Peninsula and Ellsworth Land, Antarctica

The presence of marine microfossils (diatoms) in glacier ice and ice cores has been documented from numerous sites in Antarctica, Greenland, as well as from sites in the Andes and the Altai mountains, and attributed to entrainment and transport by winds. However, their presence and diversity in snow and ice, especially in polar regions, are not well documented and still poorly understood. Here we present the first data to resolve the regional and temporal distribution of diatoms in ice cores, spanning a 20-year period across four sites in the Antarctic Peninsula and Ellsworth Land, Antarctica. We assess the regional variability in diatom composition and abundance at annual and sub-annual resolution across all four sites. These data corroborate the prevalence of contemporary marine diatoms in Antarctic Peninsula ice cores, reveal that the timing and amount of diatoms deposited vary between low- and high-elevation sites, and support existing evidence that marine diatoms have the potential to yield a novel palaeoenvironmental proxy for ice cores in Antarctica

Dimensions of Religiousness and Cancer Screening Behaviors among Church-Going Latinas

Churches are a promising setting through which to reach Latinas with cancer control efforts. A better understanding of the dimensions of religiousness that impact health behaviors could inform efforts to tailor cancer control programs for this setting. The purpose of this study was to explore relationships between dimensions of religiousness with adherence to cancer screening recommendations among church-going Latinas. Female Spanish-speaking members, aged 18 and older from a Baptist church in Boston, Massachusetts (N = 78), were interviewed about cancer screening behaviors and dimensions of religiousness. We examined adherence to individual cancer screening tests (mammography, Pap test, and colonoscopy), as well as adherence to all screening tests for which participants were age-eligible. Dimensions of religiousness assessed included church participation, religious support, active and passive spiritual health locus of control, and positive and negative religious coping. Results showed that roughly half (46 %) of the sample had not received all of the cancer screening tests for which they were age-eligible. In multivariate analyses, positive religious coping was significantly associated with adherence to all age-appropriate screening (OR = 5.30, p \u3c .01). Additional research is warranted to replicate these results in larger, more representative samples and to examine the extent to which enhancement of religious coping could increase the impact of cancer control interventions for Latinas