title: The influence of prevalent cohort bias in the association between periodontal disease progression and incident coronary heart disease.
abstract: OBJECTIVE
  In longitudinal studies, the onset of the index condition (e.g. exposure) does not always coincide with the start of a study's observation period, leading to the possibility of bias in estimation that derives from studying prevalent exposure rather than new exposure. We investigate the possible role of this bias in the relationship between periodontitis progression and coronary heart disease (CHD) among a cohort of men participating in the Veterans Administration Dental Longitudinal Study.
  
  
  METHODS
  At baseline, there were 298 men with existing (i.e., prevalent) periodontitis. During follow-up, routine dental inspection identified 163 new (i.e., incident) cases of periodontitis. Change in mean alveolar bone loss score (MBLS) served as the measure of disease progression. Tabular analyses were performed to obtain crude, stratified, and adjusted measures of the association for periodontitis cases overall and separately for prevalent and incident cases. Potential bias was evaluated by comparing estimates across these subcohorts.
  
  
  RESULTS
  Among all periodontitis cases, increasing MBLS was associated with increasing risk of CHD event. Subdividing periodontal cases into new and prevalent cases revealed that the relationship was most pronounced among incident periodontitis cases (incident rate ratio for MBLS change >0.5 = 5.4), compared with prevalent cases (incident rate ratio for MBLS change >0.5 = 2.5).
  
  
  CONCLUSIONS
  Studying prevalent cases of periodontitis underestimates the association between incidence periodontitis and CHD.
authors.affiliation: Department of Health Policy and Health Services Research, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA. Electronic address: brenda9@bu.edu.
authors.forename: Brenda
authors.initials: B
authors.lastname: Heaton
authors.affiliation: Department of Health Policy and Health Services Research, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA; Department of Environmental and Occupational Health, School of Public Health and Health Services, George Washington University, Washington, DC.
authors.forename: Katie M
authors.initials: KM
authors.lastname: Applebaum
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Rothman
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Brooks
authors.affiliation: Department of Biostatistics, Boston University School of Public Health, Boston, MA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Heeren
authors.affiliation: Department of Oral Surgery, The School of Dentistry, University of Birmingham, Birmingham, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dietrich
authors.affiliation: Department of Health Policy and Health Services Research, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA.
authors.forename: Raul I
authors.initials: RI
authors.lastname: Garcia
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D015897:Comorbidity; D003327:Coronary Disease / Q000453:epidemiology*; D018450:Disease Progression; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010518:Periodontitis / Q000453:epidemiology*; D015995:Prevalence; D014481:United States; D014493:United States Department of Veterans Affairs; D055815:Young Adult
keywords: Bias (epidemiology); Cardiovascular diseases; Cohort studies; Periodontal diseases