title: An application of multilevel modelling to longitudinal periodontal research data.
abstract: OBJECTIVE
  To introduce the concepts of random coefficient multilevel models through an application to periodontal research data.
  
  
  METHODS
  Multilevel models with random coefficients are illustrated using periodontal data that comprise four levels: repeated measurements at level-1, sites at level-2, teeth at level-3, and subjects at level-4. The study explores random coefficient models--where random variation occurs about explanatory variable coefficients. Outcomes considered are lifetime cumulative attachment loss and pocket probing depth.
  
  
  METHODS
  The study data were taken from a survey of periodontal disease involving 100 white male trainee engineers aged between 16 and 20 entering the apprentice training school at the Royal Air Force-Halton, UK.
  
  
  RESULTS
  The application of multilevel modelling to longitudinal data provides a new way of exploring old problems. The multilevel random coefficient models provide an opportunity to examine the 'linear' and 'burst' theories of periodontal disease progression, leading to the postulation that both can be unified within the multilevel framework.
  
  
  CONCLUSIONS
  The multilevel methodology illustrates how advances in the understanding of oral health can be achieved with the advent of new statistical methods
authors.affiliation: Biostatistics Unit, Eastman Dental Institute for Oral Health Care Sciences, University College London, UK. m.gilthorpe@eastman.ucl.ac.uk
authors.forename: M S
authors.initials: MS
authors.lastname: Gilthorpe
authors.forename: G S
authors.initials: GS
authors.lastname: Griffiths
authors.forename: I H
authors.initials: IH
authors.lastname: Maddick
authors.forename: A T
authors.initials: AT
authors.lastname: Zamzuri
mesh_terms: D000293:Adolescent; D000328:Adult; D018865:Dental Research / Q000379:methods* / Q000706:statistics & numerical data*; D018450:Disease Progression; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008889:Military Personnel; D015233:Models, Statistical; D010510:Periodontal Diseases / Q000453:epidemiology*; D010512:Periodontal Index; D010514:Periodontal Pocket / Q000175:diagnosis; D006113:United Kingdom / Q000453:epidemiology