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Search Results: 1 - 10 of 387611 matches for " J. O. Perry "
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Null models for network data
Patrick O. Perry,Patrick J. Wolfe
Computer Science , 2012,
Abstract: The analysis of datasets taking the form of simple, undirected graphs continues to gain in importance across a variety of disciplines. Two choices of null model, the logistic-linear model and the implicit log-linear model, have come into common use for analyzing such network data, in part because each accounts for the heterogeneity of network node degrees typically observed in practice. Here we show how these both may be viewed as instances of a broader class of null models, with the property that all members of this class give rise to essentially the same likelihood-based estimates of link probabilities in sparse graph regimes. This facilitates likelihood-based computation and inference, and enables practitioners to choose the most appropriate null model from this family based on application context. Comparative model fits for a variety of network datasets demonstrate the practical implications of our results.
Point process modeling for directed interaction networks
Patrick O. Perry,Patrick J. Wolfe
Computer Science , 2010, DOI: 10.1111/rssb.12013
Abstract: Network data often take the form of repeated interactions between senders and receivers tabulated over time. A primary question to ask of such data is which traits and behaviors are predictive of interaction. To answer this question, a model is introduced for treating directed interactions as a multivariate point process: a Cox multiplicative intensity model using covariates that depend on the history of the process. Consistency and asymptotic normality are proved for the resulting partial-likelihood-based estimators under suitable regularity conditions, and an efficient fitting procedure is described. Multicast interactions--those involving a single sender but multiple receivers--are treated explicitly. The resulting inferential framework is then employed to model message sending behavior in a corporate e-mail network. The analysis gives a precise quantification of which static shared traits and dynamic network effects are predictive of message recipient selection.
Minimax rank estimation for subspace tracking
Patrick O. Perry,Patrick J. Wolfe
Statistics , 2009, DOI: 10.1109/JSTSP.2010.2048070
Abstract: Rank estimation is a classical model order selection problem that arises in a variety of important statistical signal and array processing systems, yet is addressed relatively infrequently in the extant literature. Here we present sample covariance asymptotics stemming from random matrix theory, and bring them to bear on the problem of optimal rank estimation in the context of the standard array observation model with additive white Gaussian noise. The most significant of these results demonstrates the existence of a phase transition threshold, below which eigenvalues and associated eigenvectors of the sample covariance fail to provide any information on population eigenvalues. We then develop a decision-theoretic rank estimation framework that leads to a simple ordered selection rule based on thresholding; in contrast to competing approaches, however, it admits asymptotic minimax optimality and is free of tuning parameters. We analyze the asymptotic performance of our rank selection procedure and conclude with a brief simulation study demonstrating its practical efficacy in the context of subspace tracking.
Consistent Biclustering
Cheryl J. Flynn,Patrick O. Perry
Statistics , 2012,
Abstract: Biclustering, the process of simultaneously clustering observations and variables, is a popular and effective tool for finding structure in a high-dimensional dataset. A variety of biclustering algorithms exist, and they have been applied successfully to data sources ranging from gene expression arrays to review-website data. Currently, while biclustering appears to work well in practice, there have been no theoretical guarantees about its performance. We address this shortcoming with a theorem providing sufficient conditions for asymptotic consistency when both the number of observations and the number of variables in the dataset tend to infinity. This theorem applies to a broad range of data distributions, including Gaussian, Poisson, and Bernoulli. We demonstrate our results through a simulation study and with examples drawn from microarray analysis and collaborative filtering.
M. van Riel, Zaterdagmiddagrevolutie. Portret van de Rode Jeugd
J. Perry
BMGN : Low Countries Historical Review , 2011,
Fitness, motor competence and body composition as correlates of adolescent neck/shoulder pain: an exploratory cross-sectional study
Mark C Perry, Leon M Straker, Peter B O'Sullivan, Anne J Smith, Beth Hands
BMC Public Health , 2008, DOI: 10.1186/1471-2458-8-290
Abstract: 1608 males and females of mean age 14 years answered questions on their history of NSP (4 measures), and were tested for aerobic fitness, upper and lower limb power, trunk endurance, grip strength, shoulder flexibility, motor competence and anthropometric factors. Univariate and multivariate logistic regressions were used to test for associations between NSP and physical variables.There were significant gender differences for most physical and pain variables. After multivariate analysis, males had lower odds of NSP if they had reduced back endurance [OR: 0.66 (95% CI: 0.46–0.97)], reduced persistent control [0.42 (0.19–0.95], and increased muscle power [0.33 (0.12–0.94)], and higher odds of NSP if they had a higher basketball throw [2.47 (1.22–5.00)] and jump performance [3.47 (1.55–7.74)]. Females had lower odds for NSP if they had a reduced jump performance [0.61(0.41–0.92)], a better basketball throw [0.60(0.40–0.90)], lower shoulder flexibility [0.54 (0.30–0.98)] and a higher aerobic capacity [0.61 (0.40–0.93)], and higher odds for NSP if they had greater abdominal endurance [1.57(1.07–2.31)] and greater bimanual dexterity [1.77(1.18–2.65)]. Females showed a U shaped relationship between NSP and back endurance [low: 2.12 (1.20–3.74); high 2.12 (1.18–3.83)].Adolescent NSP was associated with fitness and motor competence, although the associations varied with gender, and their strength was limited.Neck/shoulder pain (NSP) may affect up to half of adolescents [1], leading to significant loss of function [2]. Up to 25% of adolescents with NSP experience some degree of disability [3] and 11% may require prescription drugs to manage pain [4]. Some risk factors for adolescent NSP have been identified, including high levels of computer use [5], employment [6], negative psychosocial factors [6-8], female gender [8], and sustained postures [1]. Very low and high levels of physical activity [7] are also associated with adolescent NSP. Activity levels may influence NSP dire
Self-care coping strategies in people with diabetes: a qualitative exploratory study
Margaret M Collins, Colin P Bradley, Tony O'Sullivan, Ivan J Perry
BMC Endocrine Disorders , 2009, DOI: 10.1186/1472-6823-9-6
Abstract: A maximum variation sample of 17 patients was selected from GP practices and diabetes clinics in Ireland to include patients with types 1 and 2 diabetes, various self-care regimens, and a range of diabetes complications. Data were collected by in-depth interviews; which were tape-recorded and transcribed. The transcripts were analysed using open and axial coding procedures to identify main categories, and were reviewed by an independent corroborator. Discussion of the results is made in the theoretical context of the health belief, health value, self-efficacy, and locus of control frameworks.Patients' perceptions of their self-care varied on a spectrum, displaying differences in self-care responsibilities such as competence with dietary planning, testing blood sugar and regular exercise. Three patient types could be distinguished, which were labeled: "proactive manager," a patient who independently monitors blood glucose and adjusts his/her self-care regime to maintain metabolic control; "passive follower," a patient who follows his/her prescribed self-care regime, but does not react autonomously to changes in metabolic control; and "nonconformist," a patient who does not follow most of his/her prescribed self-care regimen.Patients have different diabetes self-care coping strategies which are influenced by their self-care health value and consequently may affect their diet and exercise choices, frequency of blood glucose monitoring, and compliance with prescribed medication regimens. Particular attention should be paid to the patient's self-care coping strategy, and self-care protocols should be tailored to complement the different patient types.Diabetes is both a lifelong and a twenty-four hour a day condition. Glucose control is almost entirely in the hands of the person who lives with this condition. His/her motivation to eat, exercise, take medication, test glucose levels, and maintain a normal body weight all vie with life's other motivations.One of the biggest
Spinal pain and nutrition in adolescents - an exploratory cross-sectional study
Mark C Perry, Leon M Straker, Wendy H Oddy, Peter B O'Sullivan, Anne J Smith
BMC Musculoskeletal Disorders , 2010, DOI: 10.1186/1471-2474-11-138
Abstract: This study surveyed the spinal pain (neck and back) and nutrition (specific nutrients, broad food groups, diet quality and dietary pattern) of 1424 male and female adolescents at 14 years of age, in Western Australia.Back or neck pain were experienced by around half of the adolescents, with females more likely to experience spinal pain. Nutrition differed between sexes and deviated from optimal intakes. Vitamin B12, eggs, cereals and meat consumption were related to spinal pain in sex specific multivariate analyses including primary carer education level and adolescent waist girth and smoking.The findings of this study suggest that certain aspects of diet may have an association with spinal pain in adolescence.Spinal pain is a serious problem for adolescents, with over half having experienced some form of back or neck pain by mid adolescence[1,2] and a third experiencing a reduction in function [3]. Adolescent spinal pain also appears to be a precursor to adult spinal pain [4-6], which has well-documented personal and societal costs [7]. Identification of contributing factors is therefore warranted.Adolescent spinal pain has been shown to relate to physical factors such as obesity [8], psychosocial factors such as emotional problems [9] and lifestyle factors. Aspects of lifestyle such as very high or very low activity [10] or excessive computer use [11] have been shown to relate to adolescent spinal pain in cross-sectional studies. Moreover two longitudinal studies have shown links between adolescent spinal pain and aspects of lifestyle such as employment [12,13] and smoking [12]. However, another potentially important lifestyle factor, nutrition, has only been sparingly investigated. In the only studies to our knowledge concerning adolescent spinal pain and nutrition, Ghandour et al. [14] reported that back pain was related to high caffeine intake in adolescent girls, and Molcho et al. [15] documented that adolescents who reported going to bed hungry because there
Viewing Learning Through a New Lens: The Quantum Perspective of Learing  [PDF]
Katherine J. Janzen, Beth Perry, Margaret Edwards
Creative Education (CE) , 2012, DOI: 10.4236/ce.2012.36106
Abstract: We are living in a quantum world where virtuality allows us to transcend time and space. Boundaries, which were considered to be predetermined, are no longer absolute. This has important implications for the field of education as educators advance e-learning. However, education theory has been outpaced by practice. In this paper the authors propose a new learning perspective— the quantum perspective of learning which moves beyond current popular educational theories of constructivism (Siemens, 2005) and connectivism (Vygotsky, 1978). The five assumptions of the quantum perspective of learning are explored. Specifically, learning is multi-dimensional, occurs in various planes simultaneously, consists of potentialities which exist infinitely, is holistic/holographic in nature and is patterned within holographic realities, and learning environments are living systems. Implications that arise from this perspective are discussed.
Cross-Validation for Unsupervised Learning
Patrick O. Perry
Statistics , 2009,
Abstract: Cross-validation (CV) is a popular method for model-selection. Unfortunately, it is not immediately obvious how to apply CV to unsupervised or exploratory contexts. This thesis discusses some extensions of cross-validation to unsupervised learning, specifically focusing on the problem of choosing how many principal components to keep. We introduce the latent factor model, define an objective criterion, and show how CV can be used to estimate the intrinsic dimensionality of a data set. Through both simulation and theory, we demonstrate that cross-validation is a valuable tool for unsupervised learning.
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