Saddlepoint approximations for likelihood ratio like statistics with applications to permutation tests

We obtain two theorems extending the use of a saddlepoint approximation to multiparameter problems for likelihood ratio-like statistics which allow their use in permutation and rank tests and could be used in bootstrap approximations. In the first, we show that in some cases when no density exists, the integral of the formal saddlepoint density over the set corresponding to large values of the likelihood ratio-like statistic approximates the true probability with relative error of order $1/n$. In the second, we give multivariate generalizations of the Lugannani--Rice and Barndorff-Nielsen or $r^*$ formulas for the approximations. These theorems are applied to obtain permutation tests based on the likelihood ratio-like statistics for the $k$ sample and the multivariate two-sample cases. Numerical examples are given to illustrate the high degree of accuracy, and these statistics are compared to the classical statistics in both cases.Comment: Published in at http://dx.doi.org/10.1214/11-AOS945 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

A comparison of the accuracy of saddlepoint conditional cumulative distribution function approximations

Consider a model parameterized by a scalar parameter of interest and a nuisance parameter vector. Inference about the parameter of interest may be based on the signed root of the likelihood ratio statistic R. The standard normal approximation to the conditional distribution of R typically has error of order O(n^{-1/2}), where n is the sample size. There are several modifications for R, which reduce the order of error in the approximations. In this paper, we mainly investigate Barndorff-Nielsen's modified directed likelihood ratio statistic, Severini's empirical adjustment, and DiCiccio and Martin's two modifications, involving the Bayesian approach and the conditional likelihood ratio statistic. For each modification, two formats were employed to approximate the conditional cumulative distribution function; these are Barndorff-Nielson formats and the Lugannani and Rice formats. All approximations were applied to inference on the ratio of means for two independent exponential random variables. We constructed one and two-sided hypotheses tests and used the actual sizes of the tests as the measurements of accuracy to compare those approximations.Comment: Published at http://dx.doi.org/10.1214/074921707000000193 in the IMS Lecture Notes Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

Evaluation of Variability Concepts for Simulink in the Automotive Domain

Modeling variability in Matlab/Simulink becomes more and more important. We took the two variability modeling concepts already included in Matlab/Simulink and our own one and evaluated them to find out which one is suited best for modeling variability in the automotive domain. We conducted a controlled experiment with developers at Volkswagen AG to decide which concept is preferred by developers and if their preference aligns with measurable performance factors. We found out that all existing concepts are viable approaches and that the delta approach is both the preferred concept as well as the objectively most efficient one, which makes Delta-Simulink a good solution to model variability in the automotive domain.Comment: 10 pages, 7 figures, 6 tables, Proceedings of 48th Hawaii International Conference on System Sciences (HICSS), pp. 5373-5382, Kauai, Hawaii, USA, IEEE Computer Society, 201

A Dual Model of Open Source License Growth

Every open source project needs to decide on an open source license. This decision is of high economic relevance: Just which license is the best one to help the project grow and attract a community? The most common question is: Should the project choose a restrictive (reciprocal) license or a more permissive one? As an important step towards answering this question, this paper analyses actual license choice and correlated project growth from ten years of open source projects. It provides closed analytical models and finds that around 2001 a reversal in license choice occurred from restrictive towards permissive licenses.Comment: 14 pages, 6 figure

Portfolio of compositions (and accompanying commentary)

The first half of this commentary/thesis will explore changing perceptions of the musical work and the creative process. Ultimately, it will seek to identify and expose the myth of what we might call the ‘tyrannical composer’. That is to say, a suspicion of what is implied hierarchically by the figure of the composer and the consequences this has on critical thought, scholarship, performance and the public perception of music, new and old. By drawing upon recent research in, among other things, semiotics and mediation theory, I seek to reimagine the traditional composer-performer-audience relationship as something far more democratic and linear than is often given credit. Discussions typically reserved for overtly challenging and ‘experimental’ genres of music can here be reframed and proposed as a defence of related but contrasting styles of acoustic avant-garde composition. The above argument will be supported in the second chapter by a selection of case studies drawing upon my own portfolio of compositions. Analysis of some of these works will ask questions about composer authority and agency and draw upon my practical experience as composer of the works in question. The composer will ultimately be understood not as a dictator-like figure and privileged arbiter of the ‘musical work’, but as a democratically motivated creative agent, dialectically and collaboratively involved in the mediation and reception of the performed work

Spider phobics more easily see a spider in morphed schematic pictures

Background: Individuals with social phobia are more likely to misinterpret ambiguous social situations as more threatening, i.e. they show an interpretive bias. This study investigated whether such a bias also exists in specific phobia. Methods: Individuals with spider phobiaor social phobia, spider aficionados and non-phobic controls saw morphed stimuli that gradually transformed from a schematic picture of a flower into a schematic picture of a spider by shifting the outlines of the petals until they turned into spider legs. Participants' task was to decide whether each stimulus was more similar to a spider, a flower or to neither object while EEG was recorded. Results: An interpretive bias was found in spider phobia on a behavioral level: with the first opening of the petals of the flower anchor, spider phobics rated the stimuli as more unpleasant and arousing than the control groups and showed an elevated latent trait to classify a stimulus as a spider and a response-time advantage for spider-like stimuli. No cortical correlates on the level of ERPs of this interpretive bias could be identified. However, consistent with previous studies, social and spider phobic persons exhibited generally enhanced visual P1 amplitudes indicative of hypervigilance in phobia. Conclusion: Results suggest an interpretive bias and generalization of phobia-specific responses in specific phobia. Similar effects have been observed in other anxiety disorders, such as social phobia and posttraumatic stress disorder. © 2007 Kolassa et al; licensee BioMed Central Ltd

Comparison of Partner Assisted PNF Stretching and Strap Assisted PNF Stretching

Purpose: There are many studies comparing different methods of PNF stretching to each other and static stretching, but there are few studies comparing the use of a strap with PNF stretching. The lack of studies comparing unassisted strap PNF stretching to assisted PNF stretching for chronic increases in hamstring flexibility creates challenges in determining if using a strap is practical to recommend. Benefits of the strap include making PNF stretching more accessible to those who don’t have someone to assist them with PNF stretching, especially at home. Methods: The study involved students who attend the University of North Florida and they were broken up into an exercise professional assisted (EPA) PNF stretching (n = 6) and a strap assisted (SA) PNF stretching group (n = 9). The groups stretched four times per week for four week and joint range of motion (ROM) was assessed at the beginning, and end of the study. A t-test was utilized to determine if differences between groups as a result of the intervention. Results: There was no difference in change in hamstring ROM from the pre-test measurements to the post-test measurements within or between groups. Conclusion: These findings are inconsistent with previous research that has shown increases in hamstring ROM when doing assisted PNF stretching. These inconsistencies could be from subject sample pool (young physically active students), inter-rater reliability (2 exercise science students and one PT student), and assessment time of day (varied based on subject availability)