title: European Project on OSteoArthritis (EPOSA): methodological challenges in harmonization of existing data from five European population-based cohorts on aging.
abstract: BACKGROUND
  The European Project on OSteoArthritis (EPOSA), here presented for the first time, is a collaborative study involving five European cohort studies on aging. This project focuses on the personal and societal burden and its determinants of osteoarthritis (OA). The aim of the current report is to describe the purpose of the project, the post harmonization of the cross-national data and methodological challenges related to the harmonization process
  
  
  METHODS
  The study includes data from cohort studies in five European countries (Germany, Italy, the Netherlands, Spain and the United Kingdom) on older community-dwelling persons aged ≥ 59 years. The study design and main characteristics of the five cohort studies are described. Post harmonization algorithms are developed by finding a "common denominator" to merge the datasets and weights are calculated to adjust for differences in age and sex distribution across the datasets.
  
  
  RESULTS
  A harmonized database was developed, consisting of merged data from all participating countries. In total, 10107 persons are included in the harmonized dataset with a mean age of 72.8 years (SD 6.1). The female/male ratio is 53.3/46.7%. Some variables were difficult to harmonize due to differences in wording and categories, differences in classifications and absence of data in some countries. The post harmonization algorithms are described in detail in harmonization guidelines attached to this paper.
  
  
  CONCLUSIONS
  There was little evidence of agreement on the use of several core data collection instruments, in particular on the measurement of OA. The heterogeneity of OA definitions hampers comparing prevalence rates of OA, but other research questions can be investigated using high quality harmonized data. By publishing the harmonization guidelines, insight is given into (the interpretation of) all post harmonized data of the EPOSA study.
authors: Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, the Netherlands. l.schaap@vumc.nl
authors: Laura A
authors: LA
authors: Schaap
authors: Geeske Mee
authors: GM
authors: Peeters
authors: Elaine M
authors: EM
authors: Dennison
authors: Sabina
authors: S
authors: Zambon
authors: Thorsten
authors: T
authors: Nikolaus
authors: Mercedes
authors: M
authors: Sanchez-Martinez
authors: Estella
authors: E
authors: Musacchio
authors: Natasja M
authors: NM
authors: van Schoor
authors: Dorly Jh
authors: DJ
authors: Deeg
mesh_terms: D017677:Age Distribution; D000368:Aged; D000375:Aging; D000465:Algorithms; D015331:Cohort Studies; D016208:Databases, Factual / Q000592:standards*; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000453:epidemiology*; D017678:Sex Distribution