title: Impact of analytic conventions on outcome measures in two longitudinal studies of dental caries.
abstract: Caries increment is the primary outcome measure used in most longitudinal studies of caries. Its computation requires the adoption of specific analytic conventions for handling examiner misclassification ("reversals"), teeth lost due to caries, and multiple events such as caries initiation and progression. However, little is known about the impact of these analytic conventions on cumulative incidence and incidence density--two additional outcome measures used in longitudinal studies.
  
  
  OBJECTIVE
  We evaluated the impact of analytic conventions on caries outcome measures in two longitudinal caries studies.
  
  
  METHODS
  A secondary analysis was undertaken using data from two studies: a 2-year observational cohort study of 683 older adults and a 3-year clinical trial of 1,754 children. Crude, net and adjusted increments were compared, effects of inclusion and exclusion of teeth lost due to caries were contrasted and measures of caries initiation and progression were assessed among subgroups in each study.
  
  
  RESULTS
  Cumulative incidence indicated a high risk of caries (50% or more) in both studies but was not sensitive to subgroup differences. Increment and incidence density measures consistently revealed between-subgroup differences when subgroups had comparable numbers of teeth. For all three outcome measures, crude DFS values were larger than net DFS values. The adjusted DFS was similar to crude DFS in older adults, but similar to net DFS in children. Measurement of caries initiation and progression increased disease estimates for all three outcome measures.
  
  
  CONCLUSIONS
  In the populations studied, analytic conventions for handling examiner misclassification, teeth lost due to caries and multiple events had a greater impact on inferences than the choice of outcome measure.
authors.affiliation: Department of Dental Ecology, University of North Carolina, Chapel Hill 27599-7450, USA. gary_slade@dentistry.unc.edu
authors.forename: G D
authors.initials: GD
authors.lastname: Slade
authors.forename: D J
authors.initials: DJ
authors.lastname: Caplan
mesh_terms: D000293:Adolescent; D000368:Aged; D002648:Child; D015986:Confounding Factors, Epidemiologic; D004245:DMF Index; D003731:Dental Caries / Q000453:epidemiology*; D015340:Epidemiologic Research Design; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008875:Middle Aged; D015588:Observer Variation; D009820:Ohio / Q000453:epidemiology; D017063:Outcome Assessment, Health Care / Q000379:methods*; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D013021:South Australia / Q000453:epidemiology