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Search Results: 1 - 10 of 2705 matches for " Ralf Strobl "
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Graphical modeling of binary data using the LASSO: a simulation study
Ralf Strobl, Eva Grill, Ulrich Mansmann
BMC Medical Research Methodology , 2012, DOI: 10.1186/1471-2288-12-16
Abstract: We analyzed the Bolasso to derive graphical models in comparison with other LASSO based method. Model performance was assessed in a simulation study with random data generated via symmetric local logistic regression models and Gibbs sampling. Main outcome variables were the Structural Hamming Distance and the Youden Index.We applied the results of the simulation study to a real-life data with functioning data of patients having head and neck cancer.Bootstrap aggregating as incorporated in the Bolasso algorithm greatly improved the performance in higher sample sizes. The number of bootstraps did have minimal impact on performance. Bolasso performed reasonable well with a cutpoint of 0.90 and a small penalty term. Optimal prediction for Bolasso leads to very conservative models in comparison with AIC, BIC or cross-validated optimal penalty terms.Bootstrap aggregating may improve variable selection if the underlying selection process is not too unstable due to small sample size and if one is mainly interested in reducing the false discovery rate. We propose using the Bolasso for graphical modeling in large sample sizes.A common problem in contemporary biomedical research is the occurrence of a large number of variables that accompany relatively few observations. Thus, studying associations in high-dimensional data is not straightforward. Including all variables would result in a highly over parameterized model, computational complexity and unstable estimation of the associations [1]. This methodological problem has been solved for the domain of genomic medicine by using graphical modeling. Graphical models were identified as a promising new approach to modeling clinical data [2], and thereby the systems approach to health and disease.A promising approach to describe such complex relationships is graphical modeling. Graphical models [3] provide a probabilistic tool to display, analyze and visualize the net-like dependence structures by drawing a graph describing the con
Patients' functioning as predictor of nursing workload in acute hospital units providing rehabilitation care: a multi-centre cohort study
Martin Mueller, Stefanie Lohmann, Ralf Strobl, Christine Boldt, Eva Grill
BMC Health Services Research , 2010, DOI: 10.1186/1472-6963-10-295
Abstract: Patients' functioning at admission was assessed using the respective Acute ICF Core Set and the Barthel Index, whereas nursing workload data was collected using an established instrument. Associations between dependent and independent variables were modelled using linear regression. Variable selection was carried out using penalized regression.In patients with neurological and cardiopulmonary conditions, selected ICF categories and the Barthel Index Score explained the same variance in nursing workload (44% in neurological conditions, 35% in cardiopulmonary conditions), whereas ICF was slightly superior to Barthel Index Score for musculoskeletal conditions (20% versus 16%).A substantial fraction of the variance in nursing workload in patients with rehabilitation needs in the acute hospital could be predicted by selected categories of the Acute ICF Core Sets, or by the Barthel Index score. Incorporating ICF Core Set-based data in nursing management decisions, particularly staffing decisions, may be beneficial.Nurses play a major role in the acute care hospital by improving or maintaining the health status and functioning of patients, while minimizing their distress and suffering [1]. Since nurse staffing represents a considerable proportion of the total staffing costs in acute care hospitals [2], management decisions regarding quality and quantity of nurse staffing have important consequences for hospital budgets. The task of management is to obtain an optimal solution to the nursing care requirements of particular patient populations within an organizational unit. The cost-benefit analysis implicit in the process is essential because nurse staffing is closely associated with patient outcomes [3-5]. Furthermore, sufficient nurse staffing to avoid excessive workload is an essential requirement for occupational health of caregivers [6].Various criteria are available to determine whether the scale and composition of nurse staffing are adequate to meeting the needs of pa
Identification of aspects of functioning, disability and health relevant to patients experiencing vertigo: a qualitative study using the international classification of functioning, disability and health
Martin Mueller, Edith Schuster, Ralf Strobl, Eva Grill
Health and Quality of Life Outcomes , 2012, DOI: 10.1186/1477-7525-10-75
Abstract: We conducted a series of qualitative semi-structured face-to-face interviews using a descriptive approach. Data was analyzed using the meaning condensation procedure and then linked to categories of the International Classification of Functioning, Disability and Health (ICF).From May to July 2010 12 interviews were carried out until saturation was reached. Four hundred and seventy-one single concepts were extracted which were linked to 142 different ICF categories. 40 of those belonged to the component body functions, 62 to the component activity and participation, and 40 to the component environmental factors. Besides the most prominent aspect “dizziness” most participants reported problems within “Emotional functions (b152), problems related to mobility and carrying out the daily routine. Almost all participants reported “Immediate family (e310)” as a relevant modifying environmental factor.From the patients’ perspective, vertigo has impact on multifaceted aspects of functioning and disability, mainly body functions and activities and participation. Modifying contextual factors have to be taken into account to cover the complex interaction between the health condition of vertigo on the individuals’ daily life. The results of this study will contribute to developing standards for the measurement of functioning, disability and health relevant for patients suffering from vertigo.
Identification of ICF categories relevant for nursing in the situation of acute and early post-acute rehabilitation
Martin Mueller, Christine Boldt, Eva Grill, Ralf Strobl, Gerold Stucki
BMC Nursing , 2008, DOI: 10.1186/1472-6955-7-3
Abstract: First, in a consensus process, "Leistungserfassung in der Pflege" (LEP) nursing interventions relevant for the situation of acute and early post-acute rehabilitation were selected. Second, in an integrated two-step linking process, two nursing experts derived goals of LEP nursing interventions from their practical knowledge and selected corresponding ICF categories most relevant for patients in acute and post-acute rehabilitation (ICF Core Sets).Eighty-seven percent of ICF Core Set categories could be linked to goals of at least one nursing intervention variable of LEP. The ICF categories most frequently linked with LEP nursing interventions were respiration functions, experience of self and time functions and focusing attention. Thirteen percent of ICF Core Set categories could not be linked with LEP nursing interventions. The LEP nursing interventions which were linked with the highest number of different ICF-categories of all were "therapeutic intervention", "patient-nurse communication/information giving" and "mobilising".The ICF Core Sets for the acute hospital and early post-acute rehabilitation facilities are highly relevant for rehabilitation nursing. Linking nursing interventions with ICF Core Set categories is a feasible way to analyse nursing. Using the ICF Core Sets to describe goals of nursing interventions both facilitates inter-professional communication and respects patient's needs. The ICF may thus be a useful framework to set nursing intervention goals.The recovery of patients after an acute episode of illness or injury depends both on adequate medical treatment and on the early identification of needs for rehabilitation care. Acute rehabilitation is carried out by dedicated post-acute rehabilitation facilities, or by specialized wards within acute hospitals. Rehabilitation care in the acute situation is given individually by health professionals, mostly and typically by nurses with the goal to prevent complications and to restore functioning. In t
Distribution and determinants of functioning and disability in aged adults - results from the German KORA-Age study
Ralf Strobl, Martin Müller, Rebecca Emeny, Annette Peters, Eva Grill
BMC Public Health , 2013, DOI: 10.1186/1471-2458-13-137
Abstract: The objective of our study is to examine the frequency, distribution and determinants of functioning and disability in aged persons and to assess the contribution of diseases to the prevalence of disability.Data originate from the MONICA/KORA study, a population-based epidemiological cohort. Survivors of the original cohorts who were 65 and older were examined by telephone interview in 2009. Disability was assessed with the Health Assessment Questionnaire Disability Index (HAQ-DI). Minimal disability was defined as HAQ-DI > 0. Logistic regression was used to adjust for potential confounders and additive regression to estimate the contribution of diseases to disability prevalence.We analyzed a total of 4117 persons (51.2% female) with a mean age of 73.6 years (SD = 6.1). Minimal disability was present in 44.7% of all participants. Adjusted for age and diseases, disability was positively associated with female sex, BMI, low income, marital status, physical inactivity and poor nutritional status, but not with smoking and education. Problems with joint functions and eye diseases contributed most to disability prevalence in all age groups.In conclusion, this study could show that there are vulnerable subgroups of aged adults who should receive increased attention, specifically women, those with low income, those over 80, and persons with joint or eye diseases. Physical activity, obesity and malnutrition were identified as modifiable factors for future targeted interventions.
An RNAi-Based Approach to Down-Regulate a Gene Family In Vivo
Jeehee Kim, Aurora Badaloni, Torsten Willert, Ursula Zimber-Strobl, Ralf Kühn, Wolfgang Wurst, Matthias Kieslinger
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0080312
Abstract: Genetic redundancy poses a major problem to the analysis of gene function. RNA interference allows the down-regulation of several genes simultaneously, offering the possibility to overcome genetic redundancy, something not easily achieved with traditional genetic approaches. Previously we have used a polycistronic miR155-based framework to knockdown expression of three genes of the early B cell factor family in cultured cells. Here we develop the system further by generating transgenic mice expressing the RNAi construct in vivo in an inducible manner. Expression of the transgene from the strong CAG promoter is compatible with a normal function of the basal miRNA/RNAi machinery, and the miR155 framework readily allows inducible expression from the Rosa26 locus as shown by Gfp. However, expression of the transgene in hematopoietic cells does not lead to changes in B cell development and neuronal expression does not affect cerebellar architecture as predicted from genetic deletion studies. Protein as well as mRNA levels generated from Ebf genes in hetero- and homozygous animals are comparable to wild-type levels. A likely explanation for the discrepancy in the effectiveness of the RNAi construct between cultured cells and transgenic animals lies in the efficiency of the sequences used, possibly together with the complexity of the transgene. Since new approaches allow to overcome efficiency problems of RNAi sequences, the data lay the foundation for future work on the simultaneous knockdown of several genes in vivo.
Improvements for Vachaspati-Vilenkin-type Algorithms for Cosmic String and Disclination Formation
Karl Strobl
Physics , 1996,
Abstract: We derive various consistency requirements for Vachaspati-Vilenkin type Monte-Carlo simulations of cosmic string formation or disclination formation in liquid crystals. We argue for the use of a tetrakaidekahedral lattice in such simulations. We also show that these calculations can be carried out on lattices which are formally infinite, and do not necessitate the specification of any boundary conditions. This way string defects can be traced up to much larger lengths than on finite lattices. The simulations then fall into a more general class of simulations of self-interacting walks, which occupy the underlying lattice very sparsely. An efficient search algorithm is essential. We discuss various search strategies, and demonstrate how to implement hash tables with collision resolution by open addressing. The time to trace a string defect is then proportional only to the string length.
All Symmetries of Non-Einsteinian Gravity in $d =2$
Thomas Strobl
Physics , 1992, DOI: 10.1142/S0217751X93000576
Abstract: The covariant form of the field equations for two--dimensional $R^2$--gravity with torsion as well as its Hamiltonian formulation are shown to suggest the choice of the light--cone gauge. Further a one--to--one correspondence between the Hamiltonian gauge symmetries and the diffeomorphisms and local Lorentz transformations is established, thus proving that there are no hidden local symmetries responsible for the complete integrability of the model. Finally the constraint algebra is shown to have no quantum anomalies so that Dirac's quantization should be applicable.
Comment on Gravity and the Poincare Group
Thomas Strobl
Physics , 1993, DOI: 10.1103/PhysRevD.48.5029
Abstract: Following the approach of Grignani and Nardelli [1], we show how to cast the two-dimensional model $L \sim curv^2 + torsion^2 + cosm.const$ -- and in fact any theory of gravity -- into the form of a Poincare gauge theory. By means of the above example we then clarify the limitations of this approach: The diffeomorphism invariance of the action still leads to a nasty constraint algebra. Moreover, by simple changes of variables (e.g. in a path integral) one can reabsorb all the modifications of the original theory.
Quantization and the Issue of Time for Various Two-Dimensional Models of Gravity
Thomas Strobl
Physics , 1993, DOI: 10.1142/S0218271894000460
Abstract: It is shown that the models of 2D Liouville Gravity, 2D Black Hole- and $R^2$-Gravity are {\em embedded} in the Katanaev-Volovich model of 2D NonEinsteinian Gravity. Different approaches to the formulation of a quantum theory for the above systems are then presented: The Dirac constraints can be solved exactly in the momentum representation, the path integral can be integrated out, and the constraint algebra can be {\em explicitely} canonically abelianized, thus allowing also for a (superficial) reduced phase space quantization. Non--trivial dynamics are obtained by means of time dependent gauges. All of these approaches lead to the {\em same} finite dimensional quantum mechanical system.
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