title: Study protocol, sample characteristics, and loss to follow-up: the OPPERA prospective cohort study.
abstract: When studying incidence of pain conditions such as temporomandibular disorder (TMD), repeated monitoring is needed in prospective cohort studies. However, monitoring methods usually have limitations and, over a period of years, some loss to follow-up is inevitable. The OPPERA prospective cohort study of first-onset TMD screened for symptoms using quarterly questionnaires and examined symptomatic participants to definitively ascertain TMD incidence. During the median 2.8-year observation period, 16% of the 3,263 enrollees completed no follow-up questionnaires, others provided incomplete follow-up, and examinations were not conducted for one third of symptomatic episodes. Although screening methods and examinations were found to have excellent reliability and validity, they were not perfect. Loss to follow-up varied according to some putative TMD risk factors, although multiple imputation to correct the problem suggested that bias was minimal. A second method of multiple imputation that evaluated bias associated with omitted and dubious examinations revealed a slight underestimate of incidence and some small biases in hazard ratios used to quantify effects of risk factors. Although "bottom line" statistical conclusions were not affected, multiply-imputed estimates should be considered when evaluating the large number of risk factors under investigation in the OPPERA study.
  
  
  CONCLUSIONS
  These findings support the validity of the OPPERA prospective cohort study for the purpose of investigating the etiology of first-onset TMD, providing the foundation for other papers investigating risk factors hypothesized in the OPPERA project.
authors.affiliation: Regional Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Department of Endodontics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Eric
authors.initials: E
authors.lastname: Bair
authors.forename: Naomi C
authors.initials: NC
authors.lastname: Brownstein
authors.forename: Richard
authors.initials: R
authors.lastname: Ohrbach
authors.forename: Joel D
authors.initials: JD
authors.lastname: Greenspan
authors.forename: Ronald
authors.initials: R
authors.lastname: Dubner
authors.forename: Roger B
authors.initials: RB
authors.lastname: Fillingim
authors.forename: William
authors.initials: W
authors.lastname: Maixner
authors.forename: Shad B
authors.initials: SB
authors.lastname: Smith
authors.forename: Luda
authors.initials: L
authors.lastname: Diatchenko
authors.forename: Yoly
authors.initials: Y
authors.lastname: Gonzalez
authors.forename: Sharon M
authors.initials: SM
authors.lastname: Gordon
authors.forename: Pei-Feng
authors.initials: PF
authors.lastname: Lim
authors.forename: Margarete
authors.initials: M
authors.lastname: Ribeiro-Dasilva
authors.forename: Dawn
authors.initials: D
authors.lastname: Dampier
authors.forename: Charles
authors.initials: C
authors.lastname: Knott
authors.forename: Gary D
authors.initials: GD
authors.lastname: Slade
mesh_terms: D002985:Clinical Protocols; D015331:Cohort Studies; D006801:Humans; D015994:Incidence; D018579:Patient Selection; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013705:Temporomandibular Joint Disorders / Q000453:epidemiology* / Q000209:etiology*
keywords: Temporomandibular disorder; cohort studies; epidemiologic methods; population statistics; proportional hazards models