Two models for longitudinal item response data

Questionnaires are sometimes administered to the same sample of examinees on more than one occasion. Even when longitudinal data are available, researchers employing item response theory (IRT) often use data only from the first administration for item calibration because there is likely a lack of conditional independence between responses to the same item from the same individual. However, in many longitudinal study designs, the sample size at one occasion is too small for reliable item calibration. Thus, a longitudinal IRT model for use with repeated measures study designs is desirable. This research develops two distinct approaches to longitudinal IRT. One of these models is based on latent class analysis, while the other is based on full-information bi-factor analysis. Both account for the local dependence among items that are administered twice by introducing parameters that describe how the repeated nature of each item affects the response (separately from the effect of the latent trait). The models include parameters that describe the latent trait distribution at the second administration relative to the standardized distribution at time one and the correlation between the latent traits at two time points. The addition of these model components allows item parameters to be calibrated using available data from two occasions

Income, Poverty, and Health Insurance Coverage in the United States: 2005

This report presents data on income, poverty, and health insurance coverage in the United States based on information collected in the 2006 and earlier Annual Social and Economic Supplements (ASEC) to the Current Population Survey (CPS) conducted by the U.S. Census Bureau. Real median household income increased between 2004 and 2005. Both the number of people in poverty and the poverty rate were not statistically different between 2004 and 2005. The number of people with health insurance coverage increased, while the percentage of people with health insurance coverage decreased between 2004 and 2005. Both the number and the percentage of people without health insurance coverage increased between 2004 and 2005. These results were not uniform across demographic groups. For example, the poverty rate for non-Hispanic Whites decreased, while the overall rate was statistically unchanged. This report has three main sections— income, poverty, and health insurance coverage

Stakeholder perspectives on ecosystem-based management of the Antarctic krill fishery

Information about stakeholder aspirations is a fundamental requirement for ecosystem-based management, but the detail is often elusive, and debates may focus on simplistic opposing positions. This is exemplified by the Antarctic krill fishery, which, despite a current operational catch limit equivalent to just 1% of the estimated biomass and actual annual catches much lower than this, is the subject of a high-profile debate framed around ambiguous concepts such as sustainability. Q methodology was applied to explore the detailed views of representatives of three stakeholder sectors (the fishing industry, conservation-focused non-governmental organisations (NGOs), and scientists from seven countries involved in research on the krill-based ecosystem). The analysis distinguished two clear groupings, one of which included the views of all NGO participants while the other included the views of fishing industry participants and a subset of the scientists. Key differences between the groups included the priority given to different management measures, and to continued commercial fishing. However, the results also revealed considerable overlap between viewpoints. Both groups prioritised the maintenance of ecosystem health and recognised the importance of defining management objectives. Also, neither group prioritised a decrease in catch limits. This suggests that most participants in the study agree that management should improve but do not perceive a major problem in the ecosystem's ability to support current catch levels. Cooperation to identify shared management objectives based on stakeholder aspirations for the ecosystem might enhance progress, whereas polarised discussions about preferred management measures or ambiguous concepts are likely to impede progress

Impact of Immersive Training on Senior Chemical Engineering Students\u27 Prioritization of Process Safety Decision Criteria

Every year new safety features and regulations are employed within the process industry to reduce risks associated with operations. Despite these advancements chemical plants remain hazardous places, and the role of the engineer will always involve risk mitigation through real time decision making. Results from a previous study by Kongsvik et al., 2015 indicated that there were three types of decisions in major chemical plants: strategic decisions, operational decisions, and instantaneous decisions. The study showed the importance for improving upon engineers’ operational and instantaneous choices when tasked with quick solutions in the workforce. In this research study, we dive deeper to understand how senior chemical engineering students’ prioritize components of decision making such as budget, productivity, relationships, safety, and time, and how this prioritization may change as a result of participation in a digital immersive training environment called Contents Under Pressure. More specifically, we seek to address the following two research questions: (1) How do senior chemical engineering students prioritize safety in comparison to criteria such as budget, personal relationships, plant productivity, and time in a process safety context, and (2) How does senior chemical engineering students’ prioritization of decision making criteria (budget, personal relationships, plant productivity, safety, and time) change after exposure to a virtual process safety decision making environment? As part of this study, 187 senior chemical engineering students from three separate institutions completed a pre- and post-reflection survey around their engagement with Contents Under Pressure and asked them to rank their prioritizations of budget, productivity, relationships, safety, and time. Data was analyzed using descriptive statistics, and Friedman and Wilcoxon-sign-rank post hoc analyses were completed to determine any statistical differences between the rankings of decision making factors before and after engagement with Contents Under Pressure. Simulating process safety decision making with interactive educational supports may increase students’ understanding of genuine workplace environments and factors that contribute to process safety, without the real world hazards that result from poor decision making. By understanding how students prioritize these factors, chemical engineering curricula can be adapted to focus on the areas of process safety decision making where students need the largest improvement, thereby better preparing them to enter the engineering workforce

Item response theory detects differential item functioning between healthy and ill children in QoL measures

To demonstrate the value of item response theory (IRT) and differential item functioning (DIF) methods in examining a health-related quality of life (HRQOL) measure in children and adolescents

Detectors for the James Webb Space Telescope Near-Infrared Spectrograph I: Readout Mode, Noise Model, and Calibration Considerations

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrograph's (NIRSpec's) detectors will be read out, and present a model of how noise scales with the number of multiple non-destructive reads sampling-up-the-ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some non-ideal behaviors that have been observed in engineering grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is: (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that large-amplitude RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps.Comment: 55 pages, 10 figure

NASA's Robotic Lunar Lander Development Program

NASA Marshall Space Flight Center and the Johns Hopkins University Applied Physics Laboratory have developed several mission concepts to place scientific and exploration payloads ranging from 10 kg to more than 200 kg on the surface of the moon. The mission concepts all use a small versatile lander that is capable of precision landing. The results to date of the lunar lander development risk reduction activities including high pressure propulsion system testing, structure and mechanism development and testing, and long cycle time battery testing will be addressed. The most visible elements of the risk reduction program are two fully autonomous lander flight test vehicles. The first utilized a high pressure cold gas system (Cold Gas Test Article) with limited flight durations while the subsequent test vehicle, known as the Warm Gas Test Article, utilizes hydrogen peroxide propellant resulting in significantly longer flight times and the ability to more fully exercise flight sensors and algorithms. The development of the Warm Gas Test Article is a system demonstration and was designed with similarity to an actual lunar lander including energy absorbing landing legs, pulsing thrusters, and flight-like software implementation. A set of outdoor flight tests to demonstrate the initial objectives of the WGTA program was completed in Nov. 2011, and will be discussed

JWST Near-Infrared Detectors: Latest Test Results

The James Webb Space Telescope, an infrared-optimized space telescope being developed by NASA for launch in 2013, will utilize cutting-edge detector technology in its investigation of fundamental questions in astrophysics. JWST's near infrared spectrograph, NIRSpec utilizes two 2048 x 2048 HdCdTe arrays with Sidecar ASIC readout electronics developed by Teledyne to provide spectral coverage from 0.6 microns to 5 microns. We present recent test and calibration results for the NIRSpec flight arrays as well as data processing routines for noise reduction and cosmic ray rejection

Detectors for the James Webb Space Telescope Near-Infrared Spectrograph I: Readout Mode, Noise Model, and Calibration Considerations

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrograph's (NIRSpec's) detectors will be read out, and present a model of how noise scales with the number of multiple non-destructive reads sampling-up-the-ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some non-ideal behaviors that have been observed in engineering grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is: (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps

Environmental and societal factors affect food choice and physical activity: Rationale, influences, and leverage points

Dietary and physical activity behaviors that affect health are influenced by a wide variety of forces; changes in these behaviors require interventions and commitment to action at multiple levels.l.2 Education-based obesity-prevention strategies (e.g., mass-media promotion of healthy foods and promotion of healthy physical activity habits through schools) are viewed as the most useful and the most feasible to im~lementIm.~p licit in these strategies is the focus on the individual? Education-based strategies have met with limited long-term success in changing behavior: however, perhaps owing to a general lack of supporting environmental modifications. There is increasing recognition of the importance of the environment in shaping behavior, yet strategies that focus on changing environmental factors are much less familiar, and may therefore require partnerships with relevant sectors outside traditional health domains. As described in greater detail by Economos et al.: partnerships among researchers, educators, government, and industry have demonstrated success in smoking reduction at the population level. Interventions such as taxation and advertisement regulations have been instrumental in promoting smoking cessation in the United States and are used by agriculture and agribusiness interests to promote specific food consumption patterns. Similar models of collaborations or interventions may be successful in changing food intake and physical activity, and may potentially result in such desirable outcomes as prevention and reduction of obesity.6 It is important to appreciate the interaction among multiple environmental factors and that complex behavior changes are dependent on different influences at different levels. In Working Group 11, we took on the task of identifying broader contextual, environmental, societal, and policy variables that may improve our understanding of people's eating and physical activity behaviors and may lead to new directions for influencing shifts in behavior. Ecologic models of behavior, and most health promotion models, specify that health behaviors be influenced by biologic, demographic, psychological, sociaYcultura1, environmental, and policy variables. However, the research base that identifies specific important environmental and policy variables is very limited.'.""' Nevertheless, there are several reasons that support the need to identify environmental and policy influences on physical activity and eating behaviors