An application of multilevel modelling to longitudinal periodontal research data

Objective To introduce the concepts of random coefficient multilevel models through an application to periodontal research data. Basic research design Multilevel models with random coefficients are illustrated using periodont al 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 r andom coefficient models - where random variation occurs about explanatory variable coefficients. Outcomes considered are lifetime cumulative attachme nt loss and pocket probing depth. Participants The study data were taken fr om a survey of periodontal disease involving 100 white male trainee enginee rs aged between 16 and 20 entering the apprentice training school at the Ro yal Air Force - Halton, UK. Results The application of multilevel modelling to longitudinal data provides a new way of exploring old problems. The mul tilevel random coefficient models provide an opportunity to examine the 'li near' and 'burst' theories of periodontal disease progression, leading to t he postulation that both can be unified within the multilevel framework. Co nclusions The multilevel methodology illustrates how advances in the unders tanding of oral health can be achieved with the advent of new statistical m ethods.