title: A Method of Trigonometric Modelling of Seasonal Variation Demonstrated with Multiple Sclerosis Relapse Data.
abstract: This report describes a novel Stata-based application of trigonometric regression modelling to 55 years of multiple sclerosis relapse data from 46 clinical centers across 20 countries located in both hemispheres. Central to the success of this method was the strategic use of plot analysis to guide and corroborate the statistical regression modelling. Initial plot analysis was necessary for establishing realistic hypotheses regarding the presence and structural form of seasonal and latitudinal influences on relapse probability and then testing the performance of the resultant models. Trigonometric regression was then necessary to quantify these relationships, adjust for important confounders and provide a measure of certainty as to how plausible these associations were. Synchronization of graphing techniques with regression modelling permitted a systematic refinement of models until best-fit convergence was achieved, enabling novel inferences to be made regarding the independent influence of both season and latitude in predicting relapse onset timing in MS. These methods have the potential for application across other complex disease and epidemiological phenomena suspected or known to vary systematically with season and/or geographic location.
authors.affiliation: Department of Neurology, Royal Melbourne Hospital; Department of Medicine (RMH), The University of Melbourne; tim@burnet.edu.au.
authors.forename: Tim
authors.initials: T
authors.lastname: Spelman
authors.affiliation: Department of Neurology, Ulster Hospital.
authors.forename: Orla
authors.initials: O
authors.lastname: Gray
authors.affiliation: National Centre for Epidemiology and Population Health, Australian National University.
authors.forename: Robyn
authors.initials: R
authors.lastname: Lucas
authors.affiliation: Department of Neurology, Royal Melbourne Hospital; Department of Medicine (RMH), The University of Melbourne.
authors.forename: Helmut
authors.initials: H
authors.lastname: Butzkueven
mesh_terms: D002908:Chronic Disease; D004812:Epidemiologic Methods; D006801:Humans; D015233:Models, Statistical; D009103:Multiple Sclerosis / Q000453:epidemiology*; D012008:Recurrence; D012042:Registries; D012044:Regression Analysis; D012621:Seasons