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Search Results: 1 - 10 of 9923 matches for " Frank Konietschke "
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Nonparametric Evaluation of Quantitative Traits in Population-Based Association Studies when the Genetic Model is Unknown
Frank Konietschke, Ondrej Libiger, Ludwig A. Hothorn
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0031242
Abstract: Statistical association between a single nucleotide polymorphism (SNP) genotype and a quantitative trait in genome-wide association studies is usually assessed using a linear regression model, or, in the case of non-normally distributed trait values, using the Kruskal-Wallis test. While linear regression models assume an additive mode of inheritance via equi-distant genotype scores, Kruskal-Wallis test merely tests global differences in trait values associated with the three genotype groups. Both approaches thus exhibit suboptimal power when the underlying inheritance mode is dominant or recessive. Furthermore, these tests do not perform well in the common situations when only a few trait values are available in a rare genotype category (disbalance), or when the values associated with the three genotype categories exhibit unequal variance (variance heterogeneity). We propose a maximum test based on Marcus-type multiple contrast test for relative effect sizes. This test allows model-specific testing of either dominant, additive or recessive mode of inheritance, and it is robust against variance heterogeneity. We show how to obtain mode-specific simultaneous confidence intervals for the relative effect sizes to aid in interpreting the biological relevance of the results. Further, we discuss the use of a related all-pairwise comparisons contrast test with range preserving confidence intervals as an alternative to Kruskal-Wallis heterogeneity test. We applied the proposed maximum test to the Bogalusa Heart Study dataset, and gained a remarkable increase in the power to detect association, particularly for rare genotypes. Our simulation study also demonstrated that the proposed non-parametric tests control family-wise error rate in the presence of non-normality and variance heterogeneity contrary to the standard parametric approaches. We provide a publicly available R library nparcomp that can be used to estimate simultaneous confidence intervals or compatible multiplicity-adjusted p-values associated with the proposed maximum test.
A comparison of efficient permutation tests for unbalanced ANOVA in two by two designs--and their behavior under heteroscedasticity
Sonja Hahn,Frank Konietschke,Luigi Salmaso
Statistics , 2013,
Abstract: We compare different permutation tests and some parametric counterparts that are applicable to unbalanced designs in two by two designs. First the different approaches are shortly summarized. Then we investigate the behavior of the tests in a simulation study. A special focus is on the behavior of the tests under heteroscedastic variances.
nparLD: An R Software Package for the Nonparametric Analysis of Longitudinal Data in Factorial Experiments
Kimihiro Noguchi,Yulia R. Gel,Edgar Brunner,Frank Konietschke
Journal of Statistical Software , 2012,
Abstract: Longitudinal data from factorial experiments frequently arise in various fields of study, ranging from medicine and biology to public policy and sociology. In most practical situations, the distribution of observed data is unknown and there may exist a number of atypical measurements and outliers. Hence, use of parametric and semi-parametric procedures that impose restrictive distributional assumptions on observed longitudinal samples becomes questionable. This, in turn, has led to a substantial demand for statistical procedures that enable us to accurately and reliably analyze longitudinal measurements in factorial experiments with minimal conditions on available data, and robust nonparametric methodology offering such a possibility becomes of particular practical importance. In this article, we introduce a new R package nparLD which provides statisticians and researchers from other disciplines an easy and user-friendly access to the most up-to-date robust rank-based methods for the analysis of longitudinal data in factorial settings. We illustrate the implemented procedures by case studies from dentistry, biology, and medicine.
Pathologic Alterations of Canine and Feline Adrenal Glands  [PDF]
Nadja Herbach, Kirstin Wiele, Ulrike Konietschke, Walter Hermanns
Open Journal of Pathology (OJPathology) , 2016, DOI: 10.4236/ojpathology.2016.63017
Abstract: The aim of the study was to determine the frequency and age-dependency of adrenal changes in dogs and cats, which were dissected between 2004 and 2006 at the Institute of Veterinary Pathology, LMU Munich. The adrenal glands of 101 dogs and 159 cats were dissected free from adjacent tissue, weighed, lamellated perpendicular to its longitudinal axis and were embedded in paraffin and plastic for histologic inspection. Ageing cats most frequently showed accessory cortical nodules in the capsule, cortex and medulla, pigment deposition and shock bodies. The appearance of accessory cortical nodules and pigment deposition were linked to the age of the cats and that of shock bodies was linked to infectious diseases. Inflammatory alterations were rare and neoplastic changes were not observed. In dogs, the most frequent alterations were accessory cortical nodules in the capsule, cortex and medulla and circulatory disturbances and there was a significant linkage of the appearance of cortical nodules and pigment deposition and age. Metabolic, inflammatory and tumorous diseases were rarely observed in the dogs examined. In summary, cats and dogs show similar incidental alterations of the adrenals. Clinical relevant adrenal lesions such as atrophy or primary neoplasia were rarely diagnosed.
Solution for Rational Expectation Models Free of Complex Numbers  [PDF]
Frank Hespeler
Theoretical Economics Letters (TEL) , 2011, DOI: 10.4236/tel.2011.13011
Abstract: This paper approaches the problem of the potential for complex-valued solutions within linear macroeconomic models with rational expectations. It finds that these problems are associated with a specific solution method for the underlying model. The paper establishes that the danger of complex-valued solutions always can be eliminated by forcing those solutions to fulfill additional constraints. These constraints are essentially restrictions on the degrees of freedoms in indeterminate solutions.
A Characterization of the Optimal Management of Heterogeneous Environmental Assets under Uncertainty  [PDF]
Frank Raymond
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.25093
Abstract: The application herein involves the optimal management of renewable and nonrenewable resources within the context of a stochastic model of optimal control. By characterizing the two dimensional Bellman solution, three rules with respect to resource management are established. Within the context of coastal development, this analysis may help to explain why renewable resources may become increasingly vulnerable to random external shocks as nonrenewable resources are depleted. Although existence of an optimal closed form solution to the multi-sector Bellman model remains an open mathematical question, this analysis offers a characterization which can be applied to other scenarios in economics or finance in which two assets following stochastic processes interact.
Magnetic resonance imaging analysis of the bioabsorbable Milagro interference screw for graft fixation in anterior cruciate ligament reconstruction
K.-H. Frosch,T. Sawallich,G. Schütze,A. Losch,T. Walde,P. Balcarek,F. Konietschke,K. M. Stürmer
Strategies in Trauma and Limb Reconstruction , 2009, DOI: 10.1007/s11751-009-0063-2
Abstract: Ligament graft fixation with bioabsorbable interference screws is a standard procedure in cruciate ligament replacement. Previous screw designs may resorb incompletely, and can cause osteolysis and sterile cysts despite being implanted for several years. The aim of this study was to examine the in vivo degradation and biocompatibility of the new Milagro interference screw (Mitek, Norderstedt, Germany). The Milagro interference screw is made of 30% -TCP (TriCalcium phosphate) and 70% PLGA (Poly-lactic-co-glycolic acid). In the period between June 2005 and February 2006, 38 patients underwent graft fixation with Milagro screws in our hospital. Arthroscopic ACL reconstruction was performed using hamstring tendon grafts in all the patients. MR imaging was performed on 12 randomly selected patients out of the total of 38 at 3, 6 and 12 months after surgery. During the examination, the volume loss of the screw, tunnel enlargement, presence of osteolysis, fluid lines, edema and postoperative screw replacement by bone tissue were evaluated. There was no edema or signs of inflammation around the bone tunnels. At 3, 6 and 12 months, the tibial screws showed an average volume loss of 0, 8.1% (±7.9%) and 82.6% (±17.2%, P < 0.05), respectively. The femoral screws showed volume losses of 2.5% (±2.1%), 31.3% (±21.6%) and 92.02% (±6.3%, P < 0.05), respectively. The femoral tunnel enlargement was 47.4% (±43.8%) of the original bone tunnel volume after 12 months, and the mean tunnel volume of the tibial tunnel was 9.5% (±58.1%) compared to the original tunnel. Bone ingrowth was observed in all the patients. In conclusion, the resorption behaviour of the Milagro screw is closely linked to the graft healing process. The screws were rapidly resorbed after 6 months and, at 12 months, only the screw remnants were detectable. Moreover, the Milagro screw is biocompatible and osteoconductive, promoting bone ingrowth during resorption. Tunnel enlargement is not prevented in the first months but is reduced by bone ingrowth after 12 months.
Investigating the Suitability of Agile Methods for Requirements Development of Home Care Systems  [PDF]
Sandra Kelly, Frank Keenan
Journal of Software Engineering and Applications (JSEA) , 2010, DOI: 10.4236/jsea.2010.39104
Abstract: The ageing population in developed countries brings many benefits but also many challenges, particularly in terms of the development of appropriate technology to support their ability to remain in their own home environment. One particular challenge reported for such Home Care Systems (HCS) is the identification of an appropriate requirements development technique for dealing with the typical diverse stakeholders involved. Agile Methods (AMs) recognize this challenge and propose techniques that could be useful. This paper examines the desirable characteristics identified for requirements development in HCS and investigates the extent to which agile practices conform to these. It also sets out future work to improve the situation for the non compliant points found.
Free Anterolateral Thigh Perforator Flap for Head and Neck Cancer Resection in a Nonagenarian  [PDF]
Frank Lin, Damien Grinsell
Modern Plastic Surgery (MPS) , 2012, DOI: 10.4236/mps.2012.21001
Abstract: With an aging population, free flap reconstruction for head and neck cancer ablation in the elderly is becoming more commonplace. In nonagenarians, however, such major operations are still rarely offered due to its physiological demands. We report the first case of successful resection and reconstruction of head and neck cancer with a free perforator flap in a 96 year old patient. We feel that with careful patient and flap selection, careful preoperative workup and close collaboration between treating teams, age alone should not preclude patients from receiving the best possible curative treatment and reconstruction in head and neck cancers. Even in nonagenarians, perforator free flaps, such as the anterolateral thigh flap, can be used safely to achieve good functional and aesthetic outcomes.
Optical Modeling and Analysis of Peripheral Optics of Contact Lenses  [PDF]
Jie Shen, Frank Spors
Open Journal of Ophthalmology (OJOph) , 2012, DOI: 10.4236/ojoph.2012.23012
Abstract: Background: Degraded peripheral vision has been hypothesized to be a stimulus for the development of foveal refractive error. Contact lenses have been widely used to correct central vision, but their impacts on peripheral vision are still unknown. The purpose of this study was to use optical model software to evaluate the peripheral optics of rigid gas permeable (RGP) and soft contact lenses (SCLs) in isolation. This will better assist us in understanding their peripheral optical performances on human eyes. Methods: An optical design software package (Zemax EE) was used to model peripheral optics of Menicon RGP lens and Acuvue 2 SCLs. Profiles of sphero-cylindrical power and major higher-order aberrations were computed in 10osteps out to 40o off-axis eccentricity for –3.0 D central focal power contact lens. The results of optical modeling were analyzed and compared with previously published experimental data. Results: –3.0 D RGP lenses and SCLs had –1.4 D and –2.0 D dioptric power at 40o eccentricity, respectively. The reduced dioptric power in the periphery of the analyzed contact lenses quantitatively matched with the reduced amount of hyperopic field curvature found from experimental data when these contact lenses fitted on human eyes. Cylindrical power increased to 0.3 D ~ 0.4 D at 40o eccentricity for both lens types. In addition, both contact lens types produced higher order aberrations, namely 1.2 μm coma and 0.15 μm spherical aberration at 40o eccentricity. Conclusions: Compared to SCLs, RGP lenses with equal focal power had less dioptric power in the periphery. Both RGP lenses and SCLs produced the same amount of major higher-order aberrations with increasing of the field angle. Some of these results can be used to predict and understand the peripheral optical performance of contact lenses on human eyes.
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