KCL Statistics webinar, Autumn 2020


If you are interested in attending the webinars please contact the organiser at: kalliopi.mylona@kcl.ac.uk

15 Oct. 14:00 Eduardo García Portugués (UC3M)

Title: Uniformity tests on the hypersphere via projections

Abstract: Testing uniformity is perhaps the most fundamental problem when dealing with hyperspherical data, a datatype in which directions encode all the relevant information. In particular, testing spherical uniformity has three interesting astronomical applications regarding the study of sunspots, comets, and craters. In this talk, we introduce a projection-based class of uniformity tests on the hypersphere based on the empirical cumulative distribution function. This new class allows the derivation of new tests that neatly extend the circular-only tests by Watson, Ajne, and Rothman to the hypersphere, while also introducing the first instance of an Anderson–Darling-like test for hyperspherical data. Tractable expressions and asymptotics for the test statistics are provided, and the connection of the new class with the Sobolev class is elucidated. A simulation study evaluates the theoretical findings and evidences the competitiveness of the new tests. Applications in astronomy are shown. The talk is based on joint work (arXiv:2008.09897) with Paula Navarro-Esteban and Juan A. Cuesta-Albertos.


29 Oct. 14:00 Peter Goos (KU Leuven)

Title: Orthogonal Minimally Aliased Response Surface Designs

Abstract: Response surface designs are a core component of the response surface methodology, which is widely used in the context of product and process optimization. In this presentation, we present a new class of 3-level response surface designs, which can be viewed as matrices with entries equal to −1, 0 and +1. Because the new designs are orthogonal for the main effects and exhibit no aliasing between the main effects and the second-order effects (two-factor interactions and quadratic effects), we call them orthogonal minimally aliased response surface designs or OMARS designs. We constructed an extensive catalog of OMARS design for commonly used numbers of factors using integer programming. Also, we characterized each design in the catalog extensively in terms of estimation and prediction efficiency, identified interesting designs and investigated trade-offs between the different design evaluation criteria. Finally, we developed a multi-attribute decision algorithm to select designs from the catalog and built OMARS designs with two-level categorical factors as well. In the presentation, we compare the new OMARS designs to benchmark definitive screening designs constructed using commercial software.

12 Nov. 14:00 Jessica Barrett (University of Cambridge)

Title: Modelling longitudinal heteroscedasticity: Within-individual blood pressure variability and the risk of cardiovascular disease

Abstract: I will consider the problem of how to estimate the association between blood pressure variability and cardiovascular disease. In the clinical literature this is typically done by calculating a variability measure, e.g. the standard deviation, from a set of blood pressure measurements per individual, and including this as an explanatory variable in a regression model for the time to the first cardiovascular event. But this leads to regression dilution bias in the estimated association parameter because the variability measure is subject to measurement error. I will discuss instead the use of statistical models for within-individual variability which allow the residual variance to depend on covariates and/or random effects, e.g. mixed effects location scale models (Hedeker et al, An Application of a Mixed‐Effects Location Scale Model for Analysis of Ecological Momentary Assessment (EMA) Data, Biometrics, (2008), 64(2):627-34).


26 Nov. 14:00 Katie Severn (University of Nottingham)

Title: TBA

Abstract: TBA 

3 Dec. 14:00 Timothy I. Cannings (University of Edinburgh)

Title: TBA

Abstract: TBA 

10 Dec. 14:00 Juhyun Park (Lancaster University)

Title: TBA

Abstract: TBA