Statistical and Computational Tradeoffs in Stochastic Composite Likelihood

Maximum likelihood estimators are often of limited practical use due to the intensive computation they require. We propose a family of alternative estimators that maximize a stochastic variation of the composite likelihood function. Each of the estimators resolve the computation-accuracy tradeoff differently, and taken together they span a continuous spectrum of computation-accuracy tradeoff resolutions. We prove the consistency of the estimators, provide formulas for their asymptotic variance, statistical robustness, and computational complexity. We discuss experimental results in the context of Boltzmann machines and conditional random fields. The theoretical and experimental studies demonstrate the effectiveness of the estimators when the computational resources are insufficient. They also demonstrate that in some cases reduced computational complexity is associated with robustness thereby increasing statistical accuracy.Comment: 30 pages, 97 figures, 2 author

Asymptotic Analysis of Generative Semi-Supervised Learning

Semisupervised learning has emerged as a popular framework for improving modeling accuracy while controlling labeling cost. Based on an extension of stochastic composite likelihood we quantify the asymptotic accuracy of generative semi-supervised learning. In doing so, we complement distribution-free analysis by providing an alternative framework to measure the value associated with different labeling policies and resolve the fundamental question of how much data to label and in what manner. We demonstrate our approach with both simulation studies and real world experiments using naive Bayes for text classification and MRFs and CRFs for structured prediction in NLP.Comment: 12 pages, 9 figure

Patient Specific Alignment, Anatomy, Recovery and Outcome in Total Knee Arthroplasty

Total knee arthroplasty (TKA), despite being an otherwise highly successful medical operation, has a recurrent problem of dissatisfaction and recurrent pain rates in the 15-20% range. A variety of factors contribute to this incidence of dissatisfaction which can broadly be considered to fall into one of three groups: factors driven by the surgical outcome, pre-existing factors relating to the patients psychology, appropriateness for surgery or expectation level, and factors driven by the patient’s recovery and their management during that recovery process. With consideration to the extensive variation between patients, it is reasonable to posit that addressing patient specific factors in selection for surgery, alignment of components during surgery and post-operative management may reduce the instance of post-operative dissatisfaction. The first goal of this thesis was to understand the variation of patient anatomy as it relates to standard practice in TKA. Following the finding of extensive variation, a bio-mechanical rigid body dynamics simulation of the knee joint was developed to determine the degree to which this variation was reflected in the kinematic behaviour of the implanted knees. Later studies showed extensive kinematic variation that was responsive to variation in the alignment of the components as well as well as significantly related to patient reported outcome. Later studies further investigated how outcome related to patient selection for surgery and recovery of the patient as measured with simple activity monitoring. From this work, a pre-operative simulation assessment tool has been developed, the Dynamic Knee Score (DKS), and paired with selection and recovery management tools forms the basis of 360 Knee Systems surgical planning and patient management, which has been used in over 3,000 primary TKA’s to date

Modelling, inference and big data in biophysics

Letter to the editorIn recognition of the increasing importance of big data in biophysics, a new session called 'Modelling, inference, big data' is incorporated into the IUPAB/EBSA Congress on 18 July 2017 at Edinburgh, UK

Design of a re-entry experiment to measure aeroshell heating rates

A conceptual design review was conducted on a proposed sub-scale re-entry flight experiment. Through some statistical analysis, it was found that a fleet of 8 to 17 of the nonrecoverable re-entry capsules would be required for there to be a 95% chance of the fleet successfully carrying out a re-entry mission. The proposed capsule designs make use of a non-recoverable design. As such, it should be possible to quickly develop a small fleet of them. The experiment design looks at replicating the heat loads experienced during the hypersonic re-entry into Earth‟s atmosphere after returning from an interplanetary mission. The re-entry velocity was taken to be 16 km/s. Analysis of the resultant heat loads during atmospheric entry at this speed dictated the aeroshell size. It was shown that the extremely high aerothermodynamic heating can be effectively managed through aeroshell geometry and material selection

The Enemy of My Enemy: International Alliances Against Transnational Terrorist Organizations

A dearth of pre-existing research in the field prompted this thesis on whether traditional econometric analyses of war deterrent alliances are applicable to modern alliances for counter terror purposes. Apparent foundational and contextual differences between the two types of alliances and the costs and benefits member nations derive from each lead the author to theorize that factors contributing to the formation of each alliance are fundamentally similar. Multiple types of statistical models are used to measure variables from the Correlates of War and Polity datasets combined with custom variables in a new dataset concerning major transnational terrorist attacks and the resultant alliances in testing the effect of traditionally contributing formation factors on alliances against terrorism. The results indicate that some contributing factors are similar, extant analysis tools have utility and that further investigation is justified

CHANGES IN BACK SQUAT BAR VELOCITY AND PERCEIVED MUSCLE SORENESS FOLLOWING A STANDARDISED RUGBY LEAGUE MATCH SIMULATION

This study examined changes in back squat bar velocity and perceived muscle soreness following a rugby league match simulation protocol. Twenty male rugby league players (age: 19.8 ± 0.7 yrs) were recruited for this study. Back squat bar velocity and perceived muscle soreness of the lower body were collected on four days surrounding a match simulation: -24 h (prior to match simulation), +0 h (after the match simulation), +24 h and +48 h. Compared to baseline (-24h), there were non-significant decreases in maximum (dz=-0.50, moderate) back squat bar velocity +0 h. There was a significant increase in perceived muscle soreness at +0h only (p=0.003). Results suggest that elevated muscle soreness may not indicate impaired neuromuscular performance and highlight the importance of monitoring fatigue via multiple measures to ensure appropriate coaching decisions are made