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Key Assumption (key + assumption)
Selected AbstractsEffects of species and habitat positional errors on the performance and interpretation of species distribution modelsDIVERSITY AND DISTRIBUTIONS, Issue 4 2009Patrick E. Osborne Abstract Aim, A key assumption in species distribution modelling is that both species and environmental data layers contain no positional errors, yet this will rarely be true. This study assesses the effect of introduced positional errors on the performance and interpretation of species distribution models. Location, Baixo Alentejo region of Portugal. Methods, Data on steppe bird occurrence were collected using a random stratified sampling design on a 1-km2 pixel grid. Environmental data were sourced from satellite imagery and digital maps. Error was deliberately introduced into the species data as shifts in a random direction of 0,1, 2,3, 4,5 and 0,5 pixels. Whole habitat layers were shifted by 1 pixel to cause mis-registration, and the cumulative effect of one to three shifted layers investigated. Distribution models were built for three species using three algorithms with three replicates. Test models were compared with controls without errors. Results, Positional errors in the species data led to a drop in model performance (larger errors having larger effects , typically up to 10% drop in area under the curve on average), although not enough for models to be rejected. Model interpretation was more severely affected with inconsistencies in the contributing variables. Errors in the habitat layers had similar although lesser effects. Main conclusions, Models with species positional errors are hard to detect, often statistically good, ecologically plausible and useful for prediction, but interpreting them is dangerous. Mis-registered habitat layers produce smaller effects probably because shifting entire layers does not break down the correlation structure to the same extent as random shifts in individual species observations. Spatial autocorrelation in the habitat layers may protect against species positional errors to some extent but the relationship is complex and requires further work. The key recommendation must be that positional errors should be minimised through careful field design and data processing. [source] Sorption irreversibility of 1,4-dichlorobenzene in two natural organic matter,rich geosorbentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Michael Sander Abstract Hysteresis, a frequently observed phenomenon in sorption studies, is inconsistent with the key assumption of sorption reversibility in most fate and bioavailability models. Therefore, a study of the underlying causes of hysteresis is essential. Carbon-radiolabeled 1,4-dichlorobenzene (DCB) isotope tracer exchange was carried out at select points along the isotherms of DCB in a brown coal and a peat soil, holding total DCB concentration constant. Tracer exchange was performed both in the forward (sorption) and reverse (desorption) directions at the bulk sorption points and in the desorption direction at the corresponding bulk desorption points. Bulk DCB isotherms showed concentration-dependent hysteresis. However, tracer reequilibration in all cases was consistent with free exchange between sorbed and aqueous-phase molecules. These results rule out common experimental artifacts and demonstrate that sorption of bulk DCB is truly hysteretic (i.e., irreversible). The differences in rates between bulk and tracer sorption and desorption are consistent with the coupling of bulk DCB diffusion to other processes that retard equilibration, which we assign to matrix swelling or shrinking. Hysteresis is attributed to matrix deformation,specifically, to inelastic expansion and creation of voids accommodating sorbate molecules in the matrix, which leads to enhanced affinity in the desorption step. Comparing the results to previous results for naphthalene in the coal, we find that irreversible effects are similar for DCB and naphthalene in the coal but differ for DCB between the two sorbents. An explanation based on the different physical properties of these sorbents is provided. Solid-phase extraction of equilibrated DCB with Tenax® revealed a highly desorption-resistant fraction. While too small to account for the observed hysteresis, this fraction may represent molecules that become trapped as the matrix collapses and simultaneously stiffens during abrupt desorption. [source] Swelling and polymer erosion for poly(ethylene oxide) tablets of different molecular weights polydispersitiesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010Anna Körner Abstract The aim of the study was to determine and compare the degree of swelling and the swelling kinetics of poly(ethylene oxide) (PEO) hydrophilic matrix tablets without any additives for matrixes with different molecular weight polydispersities. A wide range of "mixed" polydisperse PEO tablets were obtained by mixing two PEO batches with average molecular weights of 105 and 2,×,106, respectively. These were compared with "single-batch" tablets with narrower mono-modal molecular weight distributions. A texture analyzer (TA) was used to determine, during the entire dissolution process, the thickness of the "gel" layer, the height of the dry tablet core and the total height of the tablet. The release of polymer from the tablet was also measured using a chromatographic method. Both the swelling histories and the polymer release rates varied strongly with molecular weight and agitation rate, whereas the rate of dissolution of the solid core varied much less with molecular weight. For single-batch and mixed tablets, tuned to give the same release rate, the swelling process was found to be very similar, regardless of the molecular polydispersity (between 1.2 and 8.8). These results support a previously proposed dissolution model with the key assumption of a constant critical viscosity, independent of time or polymer molecular weight, at the surface of the gel layer of a dissolving tablet. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1225,1238, 2010 [source] Signaling in Political Budget Cycles: How Far Are You Willing to Go?JOURNAL OF PUBLIC ECONOMIC THEORY, Issue 2 2005JORGE MIGUEL STREB A key assumption in the literature on political cycles with rational voters and opportunistic politicians is that opportunism is common knowledge. In this framework, political cycles have been interpreted as a signal of competency. However, if opportunism is not common knowledge, cycles may no longer indicate competency, but rather opportunism. This is because highly opportunistic incumbents are willing to go farther to be reelected. Since political cycles require discretionality to reallocate budget items, a decrease of discretionality curbs cycles. It may also make elections more effective at selecting competent incumbents. [source] Motives for Intergenerational Transfers: New Test for ExchangeAMERICAN JOURNAL OF ECONOMICS AND SOCIOLOGY, Issue 2 2010Jingshu Wang The question of motives for private transfers is one with important policy implications. The evidence from empirical literature has been mixed. This study proposes new tests and evidence of the "exchange motive." It examines the key assumption on which the exchange motive model is built: that a donor's behavior is determined by his/her own expectation of receiving inter-vivos transfers or bequests in return. Results from national data show that adult children's time transfers to their aging parents were positively associated with their expectation of inter-vivos financial transfers, but not with their expectation of receiving bequests. [source] Primary productivity can affect mammalian body size frequency distributionsOIKOS, Issue 2 2001Birgitta Aava Frequency distributions of mammal body sizes in large-scale assemblages have often been found to show a positive skew. In an attempt to explain this pattern, a model has been put forward which incorporates energetic constraints on fitness and thereby predicts optimal body sizes corresponding to the mode of the distribution. A key assumption of the model is that energy is unlimited. However, if energy is limited, the input of energy into a herbivorous mammal community should influence the shape of the frequency distribution. Thus, I propose that increases in primary productivity will decrease the variation of body size and increase the mean body size in a distribution. So, in low-productivity environments we should see a predominance of small-sized species, but with a great variation of body sizes due to limitations of resources (energy). I tested this hypothesis using the herbivorous mammal fauna (rodents, bats and marsupials) in seven biomes of Australia. Because herbivorous marsupials generally are fairly large-bodied while rodents and bats are small-sized and because marsupials also have a different mode of reproduction from placental mammals, the hypothesis was also tested on placental mammals and marsupials separately. There was no clear mode for the entire assemblage in any biome, but as primary productivity increased, the variation of body masses decreased and the mean body mass of the distribution increased. Body mass distributions of both placental mammals and marsupials displayed clear modes. Placental mammals also showed an increase in mean body mass. The variation in body mass of marsupials was highest for the intermediately productive biomes. Primary productivity does seem to have some effect on mammalian body mass in this case, but the results here need to be complemented with studies of other assemblages before any general conclusions can be drawn. It is also important to distinguish which taxa are affected in a heterogeneous assemblage like the Australian herbivorous mammal fauna. [source] Participation in Policy Streams: Testing the Separation of Problems and Solutions in Subnational Policy SystemsPOLICY STUDIES JOURNAL, Issue 2 2010Scott E. Robinson The multiple streams theory of national policymaking has been influential in the study of public administration and public policy,if not without a fair bit of controversy. While some laud the model for its openness to the important role of policy entrepreneurs and the irrationalities of the decision-making processes, others criticize the model for its lack of readily testable propositions. This article identifies a series of testable propositions in the multiple streams model (particularly that discussed by Kingdon). We assess whether participation in local policymaking (focusing on school district policymaking related to violence prevention) is characterized by "separate streams" of participants or is dominated by organized participants like interest groups or policy specialists. We found evidence of unity (rather than separation) in the policymaking process and scant evidence of elite, organized interests dominating the policymaking process. The results call into question a key assumption of the multiple streams model. [source] Analysis of fluid-structure interaction in low pressure MEMS by Integral EquationsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Attilio FrangiArticle first published online: 25 FEB 200 The evaluation of gas dissipation occurring in inertial polysilicon MEMS is addressed focusing the attention on the free,molecule flow. In this regime, which is very often of interest for industrial applications, collisions between molecules can be neglected and the momentum transfer to the moving shuttle can be easily computed. Since the surfaces of silicon MEMS are generally very rough, a complete diffusion model is adopted to describe the wall,molecule interaction. A Boundary Integral Equation approach is proposed and it is shown that the introduction of the key assumption of small perturbations is crucial in the development of a robust and fast numerical tool. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Essentials of Baccalaureate Nursing Education for Entry-Level Community/Public Health NursingPUBLIC HEALTH NURSING, Issue 4 2010Education Committee of the Association of Community Health Nurse Educators ABSTRACT Community/public health nursing (C/PHN) educators and practitioners need a framework from which to plan, implement, and evaluate curriculum and community-based practice. The Association of Community Health Nursing Educators (ACHNE) periodically updates the Essentials of Baccalaureate Nursing Education for Entry Level Community/Public Health Nursing to reflect changes in core knowledge, basic competencies, and practice. This update reflects relevance to 21st-century health care and to national trends influencing nursing education. The 2009 revision is based on critical analysis of key C/PHN literature and input from public health nursing educators and practitioners. A key assumption is that a baccalaureate nursing degree is the minimum requirement for professional C/PHN. Fifteen essential concepts for baccalaureate nursing education are delineated along with related competencies. Newly defined essentials include communication, social justice, and emergency preparedness, response, and recovery. Issues related to didactic and clinical experiences are addressed. The ACHNE Essentials is an important guide for baccalaureate education curriculum planning and evaluation. The Essentials may be useful as a baseline from which to develop competencies of graduate nursing programs. The document is also useful for guiding practice setting orientation and professional development. [source] Score Test for Conditional Independence Between Longitudinal Outcome and Time to Event Given the Classes in the Joint Latent Class ModelBIOMETRICS, Issue 1 2010Hélène Jacqmin-Gadda Summary Latent class models have been recently developed for the joint analysis of a longitudinal quantitative outcome and a time to event. These models assume that the population is divided in,G,latent classes characterized by different risk functions for the event, and different profiles of evolution for the markers that are described by a mixed model for each class. However, the key assumption of conditional independence between the marker and the event given the latent classes is difficult to evaluate because the latent classes are not observed. Using a joint model with latent classes and shared random effects, we propose a score test for the null hypothesis of independence between the marker and the outcome given the latent classes versus the alternative hypothesis that the risk of event depends on one or several random effects from the mixed model in addition to the latent classes. A simulation study was performed to compare the behavior of the score test to other previously proposed tests, including situations where the alternative hypothesis or the baseline risk function are misspecified. In all the investigated situations, the score test was the most powerful. The methodology was applied to develop a prognostic model for recurrence of prostate cancer given the evolution of prostate-specific antigen in a cohort of patients treated by radiation therapy. [source] Estimation of Rates of Births, Deaths, and Immigration from Mark,Recapture DataBIOMETRICS, Issue 1 2009R. B. O'Hara Summary The analysis of mark,recapture data is undergoing a period of development and expansion. Here we contribute to that by presenting a model which includes both births and immigration, as well as the usual deaths. Data come from a long-term study of the willow tit (Parus montanus), where we can assume that all births are recorded, and hence immigrants can also be identified as birds captured as adults for the first time. We model the rates of immigration, birth rate per parent, and death rates of juveniles and adults. Using a hierarchical model allows us to incorporate annual variation in these parameters. The model is fitted to the data using Markov chain Monte Carlo, as a Bayesian analysis. In addition to the model fitting, we also check several aspects of the model fit, in particular whether survival varies with age or immigrant status, and whether capture probability is affected by previous capture history. The latter check is important, as independence of capture histories is a key assumption that simplifies the model considerably. Here we find that the capture probability depends strongly on whether the individual was captured in the previous year. [source] Capture,Recapture Studies Using Radio Telemetry with Premature Radio-Tag FailureBIOMETRICS, Issue 3 2005Laura Cowen Summary Radio tags, because of their high detectability, are often used in capture,recapture studies. A key assumption is that radio tags do not cease functioning during the study. Radio-tag failure before the end of a study can lead to underestimates of survival rates. We develop a model to incorporate secondary radio-tag failure data. This model was applied to chinook smolts (Oncorhynchus tshawytscha) on the Columbia River, Washington. Estimates of fish survival from this model were much larger than those from the standard Cormack,Jolly,Seber analysis. [source] Latent Pattern Mixture Models for Informative Intermittent Missing Data in Longitudinal StudiesBIOMETRICS, Issue 2 2004Haiqun Lin Summary. A frequently encountered problem in longitudinal studies is data that are missing due to missed visits or dropouts. In the statistical literature, interest has primarily focused on monotone missing data (dropout) with much less work on intermittent missing data in which a subject may return after one or more missed visits. Intermittent missing data have broader applicability that can include the frequent situation in which subjects do not have common sets of visit times or they visit at nonprescheduled times. In this article, we propose a latent pattern mixture model (LPMM), where the mixture patterns are formed from latent classes that link the longitudinal response and the missingness process. This allows us to handle arbitrary patterns of missing data embodied by subjects' visit process, and avoids the need to specify the mixture patterns a priori. One assumption of our model is that the missingness process is assumed to be conditionally independent of the longitudinal outcomes given the latent classes. We propose a noniterative approach to assess this key assumption. The LPMM is illustrated with a data set from a health service research study in which homeless people with mental illness were randomized to three different service packages and measures of homelessness were recorded at multiple time points. Our model suggests the presence of four latent classes linking subject visit patterns to homeless outcomes. [source] An electron-flow model can predict complex redox reactions in mixed-culture fermentative BioH2: Microbial ecology evidenceBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009Hyung-Sool Lee Abstract We developed the first model for predicting community structure in mixed-culture fermentative biohydrogen production using electron flows and NADH2 balances. A key assumption of the model is that H2 is produced only via the pyruvate decarboxylation-ferredoxin-hydrogenase pathway, which is commonly the case for fermentation by Clostridium and Ethanoligenens species. We experimentally tested the model using clone libraries to gauge community structures with mixed cultures in which we did not pre-select for specific bacterial groups, such as spore-formers. For experiments having final pHs 3.5 and 4.0, where H2 yield and soluble end-product distribution were distinctly different, we established stoichiometric reactions for each condition by using experimentally determined electron equivalent balances. The error in electron balancing was only 3% at final pH 3.5, in which butyrate and acetate were dominant organic products and the H2 yield was 2.1,mol,H2/mol,glucose. Clone-library analysis showed that clones affiliated with Clostridium sp. BL-22 and Clostridium sp. HPB-16 were dominant at final pH 3.5. For final pH 4.0, the H2 yield was 0.9,mol,H2/mol,glucose, ethanol, and acetate were the dominant organic products, and the electron balance error was 13%. The significant error indicates that a second pathway for H2 generation was active. The most abundant clones were affiliated with Klebsiella pneumoniae, which uses the formate-cleavage pathway for H2 production. Thus, the clone-library analyses confirmed that the model predictions for when the pyruvate decarboxylation-ferredoxin-hydrogenase pathway was (final pH 3.5) or was not (final pH 4.0) dominant. With the electron-flow model, we can easily assess the main mechanisms for H2 formation and the dominant H2 -producing bacteria in mixed-culture fermentative bioH2. Biotechnol. Bioeng. 2009; 104: 687,697 © 2009 Wiley Periodicals, Inc. [source] Screening for type 2 diabetes: an update of the evidenceDIABETES OBESITY & METABOLISM, Issue 10 2010R. K. Simmons A growing body of evidence on diabetes screening has been published during the last 10 years. Type 2 diabetes meets many but not all of the criteria for screening. Concerns about potential harms of screening have largely been resolved. Screening identifies a high-risk population with the potential to gain from widely available interventions. However, in spite of the findings of modelling studies, the size of the benefit of earlier initiation of treatment and the overall cost-effectiveness remains uncertain, in contrast to other screening programmes (such as for abdominal aortic aneurysms) that are yet to be fully implemented. There is also uncertainty about optimal specifications and implementation of a screening programme, and further work to complete concerning development and delivery of individual- and population-level preventive strategies. While there is growing evidence of the net benefit of earlier detection of individuals with prevalent but undiagnosed diabetes, there remains limited justification for a policy of universal population-based screening for type 2 diabetes at the present time. Data from ongoing studies should inform the key assumptions in existing modelling studies and further reduce uncertainty. [source] Methods to account for spatial autocorrelation in the analysis of species distributional data: a reviewECOGRAPHY, Issue 5 2007Carsten F. Dormann Species distributional or trait data based on range map (extent-of-occurrence) or atlas survey data often display spatial autocorrelation, i.e. locations close to each other exhibit more similar values than those further apart. If this pattern remains present in the residuals of a statistical model based on such data, one of the key assumptions of standard statistical analyses, that residuals are independent and identically distributed (i.i.d), is violated. The violation of the assumption of i.i.d. residuals may bias parameter estimates and can increase type I error rates (falsely rejecting the null hypothesis of no effect). While this is increasingly recognised by researchers analysing species distribution data, there is, to our knowledge, no comprehensive overview of the many available spatial statistical methods to take spatial autocorrelation into account in tests of statistical significance. Here, we describe six different statistical approaches to infer correlates of species' distributions, for both presence/absence (binary response) and species abundance data (poisson or normally distributed response), while accounting for spatial autocorrelation in model residuals: autocovariate regression; spatial eigenvector mapping; generalised least squares; (conditional and simultaneous) autoregressive models and generalised estimating equations. A comprehensive comparison of the relative merits of these methods is beyond the scope of this paper. To demonstrate each method's implementation, however, we undertook preliminary tests based on simulated data. These preliminary tests verified that most of the spatial modeling techniques we examined showed good type I error control and precise parameter estimates, at least when confronted with simplistic simulated data containing spatial autocorrelation in the errors. However, we found that for presence/absence data the results and conclusions were very variable between the different methods. This is likely due to the low information content of binary maps. Also, in contrast with previous studies, we found that autocovariate methods consistently underestimated the effects of environmental controls of species distributions. Given their widespread use, in particular for the modelling of species presence/absence data (e.g. climate envelope models), we argue that this warrants further study and caution in their use. To aid other ecologists in making use of the methods described, code to implement them in freely available software is provided in an electronic appendix. [source] Gone too far,or not far enough?EUROPEAN JOURNAL OF PERSONALITY, Issue 1 2002Comments on the article by Ashton, Lee (2001) Ashton and Lee argue that Honesty should be added to the Big Five model of personality as a sixth factor, and present a theoretical framework for interpreting Big Five factors and Honesty that helps make sense of the proposed six-factor structure. The attempt by Ashton and Lee to go beyond the Big Five is applauded, but numerous problems are evident. Adding Honesty to the Big Five is plausible only if one ignores key assumptions that the Big Five model consists of independent factors that are candidates for pervasive lexical universals. The proposal does not take into account significant deviations from the Anglo-Germanic Big Five that have occurred in emic studies of languages having their origin outside of northern Europe, nor potential substantive interpretations of the widely replicated Negative Valence factor. Future studies should seek improvements or alternatives to the Big Five in a way that keeps constituent factors well discriminated from one another and enhances the likelihood of ubiquity across diverse languages and cultures. Copyright © 2002 John Wiley & Sons, Ltd. [source] An Anisotropic Model for Spatial ProcessesGEOGRAPHICAL ANALYSIS, Issue 1 2008Minfeng Deng One of the key assumptions in spatial econometric modeling is that the spatial process is isotropic, which means that direction is irrelevant in the specification of the spatial structure. On the one hand, this assumption largely reduces the complexity of the spatial models and facilitates estimation and interpretation; on the other hand, it appears rather restrictive and hard to justify in many empirical applications. In this article a very general anisotropic spatial model, which allows for a high level of flexibility in the spatial structure, is proposed. This new model can be estimated using maximum likelihood and its asymptotic properties are derived at length. When the model is applied to the well-known 1970 Boston housing prices data, it significantly outperforms the isotropic spatial lag model. It also provides interesting additional insights into the price determination process in the properties market. Finally, a Monte Carlo simulation study is used to confirm the optimal properties of the model. [source] Female common lizards (Lacerta vivipara) do not adjust their sex-biased investment in relation to the adult sex ratioJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2005J.-F. LE GALLIARD Abstract Sex allocation theory predicts that facultative maternal investment in the rare sex should be favoured by natural selection when breeders experience predictable variation in adult sex ratios (ASRs). We found significant spatial and predictable interannual changes in local ASRs within a natural population of the common lizard where the mean ASR is female-biased, thus validating the key assumptions of adaptive sex ratio models. We tested for facultative maternal investment in the rare sex during and after an experimental perturbation of the ASR by creating populations with female-biased or male-biased ASR. Mothers did not adjust their clutch sex ratio during or after the ASR perturbation, but produced sons with a higher body condition in male-biased populations. However, this differential sex allocation did not result in growth or survival differences in offspring. Our results thus contradict the predictions of adaptive models and challenge the idea that facultative investment in the rare sex might be a mechanism regulating the population sex ratio. [source] Towards a Richer Conception of Vocational PreparationJOURNAL OF PHILOSOPHY OF EDUCATION, Issue 1 2003Gerard Lum This paper identifies the key assumptions underpinning current arrangements in vocational education and training (VET) in the UK. These assumptions, and the idea of vocational capability they denote, are rejected in favour of a more coherent conception,a conception centred not on the traditional dichotomy of ,knowing how-knowing that' but on what I refer to as the ,constitutive understandings' from which both practical and theoretical capabilities can be seen to derive. It is argued that an account of vocational capability in these terms suggests a far richer conception of vocational preparation than current arrangements are able to admit. [source] Measuring the hospital practice environment: A Canadian contextRESEARCH IN NURSING & HEALTH, Issue 4 2002Carole A. Estabrooks Abstract The primary purpose of this study is to document the psychometric properties of the revised Nursing Work Index (NWI-R) in the context of a large Canadian sample of registered nurses. A self-administered survey containing the NWI-R was completed by 17,965 registered nurses working in 415 hospitals in three Canadian provinces. Using exploratory principal components analysis, with a forced one-factor solution, the practice environment index was obtained. In addition, key assumptions were tested from previous work about the rationale for the aggregation of NWI-R responses. In the Canadian context the one-factor solution provides a parsimonious index of the practice environment of registered nurses working in acute care hospitals. Further work is needed to determine the predictive capability of this index and its relevance to cross-national organizational contexts. © 2002 Wiley Periodicals, Inc. Res Nurs Health 25:256,268, 2002 [source] OPERATIONALIZING OPPORTUNITIES AND CREATING PUBLICS IN SALVADORAN CHURCHES: FINDINGS FROM AN ETHNOGRAPHIC PROCESS EVALUATIONANNALS OF ANTHROPOLOGICAL PRACTICE, Issue 1 2010James Huff This article explores how one faith-based nonprofit organization and its various Pentecostal and evangelical church partners in El Salvador are creating associational contexts within which local community development projects are identified and implemented. Observational and interview data derived from a process evaluation of a project identification exercise are examined to explore how different community and organizational stakeholders attempt to implement local development initiatives that will presumably build on local assets and associations. The study details the patterns of participation that emerged as members of local churches negotiated with their neighbors over how to best direct social change in their community. Corresponding analysis of interview data portrays how these same actors relied on diverse social logics,which are both religious and practical in nature,to make sense of and assess some of the key assumptions of a particular form of faith-based development. The case is a good example of how faith-based organizations play key roles in the formation of publics, wherein actors from diverse networks come together to deliberate over the aims and outcomes of local development projects in contemporary El Salvador. [source] Financial Impact of Emergency Department UltrasoundACADEMIC EMERGENCY MEDICINE, Issue 7 2009Olanrewaju A. Soremekun MD Abstract Objectives:, There is limited information on the financial implications of an emergency department ultrasound (ED US) program. The authors sought to perform a fiscal analysis of an integrated ED US program. Methods:, A retrospective review of billing data was performed for fiscal year (FY) 2007 for an urban academic ED with an ED US program. The ED had an annual census of 80,000 visits and 1,101 ED trauma activations. The ED is a core teaching site for a 4-year emergency medicine (EM) residency, has 35 faculty members, and has 24-hour availability of all radiology services including formal US. ED US is utilized as part of evaluation of all trauma activations and for ED procedures. As actual billing charges and reimbursement rates are institution-specific and proprietary information, relative value units (RVUs) and reimbursement based on the Centers for Medicare & Medicaid Services (CMS) 2007 fee schedule (adjusted for fixed diagnosis-related group [DRG] payments and bad debt) was used to determine revenue generated from ED US. To estimate potential volume, assumptions were made on improvement in documentation rate for diagnostic scans (current documentation rates based on billed volume versus diagnostic studies in diagnostic image database), with no improvements assumed for procedural ED US. Expenses consist of three components,capital costs, training costs, and ongoing operational costs,and were determined by institutional experience. Training costs were considered sunken expenses by this institution and were thus not included in the original return on investment (ROI) calculation, although for this article a second ROI calculation was done with training cost estimates included. For the purposes of analysis, certain key assumptions were made. We utilized a collection rate of 45% and hospitalization rates (used to adjust for fixed DRG payments) of 33% for all diagnostic scans, 100% for vascular access, and 10% for needle placement. An optimal documentation rate of 95% was used to estimate potential revenue. Results:, In FY 2007, 486 limited echo exams of abdomen (current procedural terminology [CPT] 76705) and 480 limited echo cardiac exams were performed (CPT 93308) while there were 78 exams for US-guided vascular access (CPT 76937) and 36 US-guided needle placements when performing paracentesis, thoracentesis, or location of abscess for drainage (CPT 76492). Applying the 2007 CMS fee schedule and above assumptions, the revenue generated was 578 RVUs and $35,541 ($12,934 in professional physician fees and $22,607 in facility fees). Assuming optimal documentation rates for diagnostic ED US scans, ED US could have generated 1,487 RVUs and $94,593 ($33,953 in professional physician fees and $60,640 in facility fees). Program expenses include an initial capital expense (estimated at $120,000 for two US machines) and ongoing operational costs ($68,640 per year to cover image quality assurance review, continuing education, and program maintenance). Based on current revenue, there would be an annual operating loss, and thus an ROI cannot be calculated. However, if potential revenue is achieved, the annual operating income will be $22,846 per year with an ROI of 4.9 years to break even with initial investment. Conclusions:, Determining an ROI is a required procedure for any business plan for establishing an ED US program. Our analysis demonstrates that an ED US program that captures charges for trauma and procedural US and achieves the potential billing volume breaks even in less than 5 years, at which point it would generate a positive margin. [source] Charting the future course of rural health and remote health in Australia: Why we need theoryAUSTRALIAN JOURNAL OF RURAL HEALTH, Issue 2 2010Lisa Bourke Abstract Objective:,This paper argues that rural and remote health is in need of theoretical development. Design:,Based on the authors' discussions, reflections and critical analyses of literature, this paper proposes key reasons why rural and remote health warrants the development of theoretical frameworks. Results:,The paper cites five reasons why theory is needed: (i) theory provides an approach for how a topic is studied; (ii) theory articulates key assumptions in knowledge development; (iii) theory systematises knowledge, enabling it to be transferable; (iv) theory provides predictability; and (v) theory enables comprehensive understanding. Conclusion:,This paper concludes with a call for theoretical development in both rural and remote health to expand its knowledge and be more relevant to improving health care for rural Australians. [source] Effect of inorganic carbon on photoautotrophic growth of microalga Chlorococcum littoraleBIOTECHNOLOGY PROGRESS, Issue 2 2009Masaki Ota Abstract The growth rate of a highly CO2 -tolerant green alga, Chlorococcum littorale, was investigated in semi-batch cultures at a temperature of 22°C, a light intensity of 170 ,mol-photon m,2 s,1 and CO2 concentrations ranging from 1 to 50% (v/v) at atmospheric pressure. In the experiments, solutions were bubbled with CO2 and N2 gas mixtures to adjust CO2 concentrations to minimize the influence of O2. Growth rate, which was defined in terms of a specific growth rate ,, decreased with increasing CO2 concentration at the conditions studied. The inhibition of growth by CO2 gas could be attributed to the concentration of inorganic carbon in the culture medium. A growth model is proposed where key assumptions are the formation of bicarbonate ion HCO as substrate for algal growth and equilibrium between CO2 inhibitor. The proposed growth model based on the Monod equation agreed with the experimental data to within 5% and provides better correlation than the conventional inhibition model, especially in the high CO2 concentration region. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] An Economic Analysis of the Returns to Canadian Swine Research: 1974,97CANADIAN JOURNAL OF AGRICULTURAL ECONOMICS, Issue 2 2001Greg Thomas This paper reports a new set of estimates of the returns to swine research in Canada. These estimates are obtained using Agriculture and Agri-Food Canada's Canadian Regional Agricultural Model (CRAM). Positive Mathematical Programming is incorporated into the model for use in this study. The CRAM allows the effects of supply shifts from technological change in the hog industry to interact with product and factor market conditions in the rest of Canadian agriculture. Extensive sensitivity analysis is conducted to examine the robustness of the return estimates under variations in some of the key assumptions employed in the analysis. The costs of public and private sector swine research are estimated. Public sector research costs are inclusive of the marginal excess burden of taxation. Overall, the estimated benefits from Canadian swine research are high relative to the estimated costs for the time period considered. Previous estimates of the returns to Canadian swine research were obtained by Huot et al. (1989) with a partial equilibrium model that did not allow for intra-sectoral resource use adjustments. The estimated returns obtained in the present study are generally higher than those obtained by Huot et al. For example, the estimates obtained from the direct application of the econometrically estimated supply function in this study gave an internal rate of return of about 124% and a benefit-cost ratio of 22.4 to 1. Huot et al reported comparable estimates of about 43% for the internal rate of return and 6,7 to 1 for the benefit-cost ratio. The differences in returns are not solely attributable to the use of a multi-market versus a single-market partial equilibrium approach. There are also differences in the estimates of the marginal excess burden of taxation between the two studies. L'analyse que void présente une nouvelle série d'estimations quant au rendement de la recherche porcine au Canada. Ces estimations dérivent du Modèle d'analyse régionale de l'agriculture du Canada (MARAC) du ministère canadien de l'Agriculture et de l'Agroalimentaire. Aux fins de la présente étude, on avait intégré au modèle une programmation mathématique positive. Le MARAC autorise l'interaction entre les retombées d'une modification de l'offre attribuable au virage technologique de l'industrie porcine et les conditions du marché des produits et des facteurs dans le reste de l'agriculture canadienne. Les auteurs ont effectué une analyse de sensibilité poussée en vue d'établir la robustesse de leurs estimations quand variaient quelques-unes des principales hypotheses de l'analyse. On a estimé le coût de la recherche sur les pores poursuivie par les secteurs public et privé. Dans le secteur public, le coût de la recherche incluait une charge fiscale légérement excessive. Dans l'ensemble, la recherche sur les porcs entreprise au Canada a rapporté beaucoup comparativement à ce qu'elle a coûté pendant la période à l'étude. Les estimations antérieures, établies par Huot et ses collaborateurs (1989), venaient d'un modèle àéquilibre partiel ne permettant aucun ajustement pour l'utilisation intra-sectorielle des ressources. Les revenus estimés ici sont généralement plus élevés que ceux de Huot et de ses collaborateurs. Ainsi, une application directe de l'offre estimée par des méthodes économétriques à l'analyse donne un taux de rendement interne d'environ 124 % et un indice de rentabilité de 22,4 pour 1. À titre de comparaison, Huot et ses collaborateurs rapportent des résultats d'environ 43 % pour le taux de rendement interne et de 6 à 7 pour 1 en ce qui concerne l'indice de rentabilité. Pareil écart ne résulte pas uniquement du choix d'un modèle àéquilibre partiel reposant sur plusieurs marchés au lieu d'un seul; on relève aussi des variations dans l'estimation du léger excès de la charge fiscale entre les deux études. [source] | ||||||||||||||||||||||||||||