title: A comparative study demonstrated that prevalence figures on multimorbidity require cautious interpretation when drawn from a single database.
abstract: OBJECTIVE
  We investigated the degree of comparability of the prevalence of chronic diseases and disease combinations in the elderly in two databases comparable with regard to diseases included, sex and age of the patients (65-85 years), and cutoff score for case definition.
  
  
  METHODS
  One study is based on chart-supported interviews with the primary care physicians within a cohort study of 3,189 multimorbid elderly patients. The second study analyzed claims data from ambulatory care delivered to the multimorbid members of one German Health Insurance (n = 70,031). Multimorbidity was defined by the presence of three or more chronic conditions from an identical list of 46 diseases.
  
  
  RESULTS
  The difference of the median number of chronic conditions was 1 (mean 6.7 vs. 5.7). The prevalences of individual conditions were approximately one-third lower in the claims data, but the relative rank order corresponded well between the two databases. These relatively small prevalence differences cumulate when combinations of chronic conditions are investigated, for example, the prevalence differences between the two databases increased to nearly 100% for triadic combinations and nearly 170% for quartets.
  
  
  CONCLUSIONS
  The study shows that conclusions regarding the prevalence of combinations of diseases should be drawn with caution when based on a single database.
authors.affiliation: Institute of Primary Medical Care, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany. bussche@uke.de
authors.forename: Hendrik
authors.initials: H
authors.lastname: van den Bussche
authors.forename: Ingmar
authors.initials: I
authors.lastname: Schäfer
authors.forename: Birgitt
authors.initials: B
authors.lastname: Wiese
authors.forename: Anne
authors.initials: A
authors.lastname: Dahlhaus
authors.forename: Angela
authors.initials: A
authors.lastname: Fuchs
authors.forename: Jochen
authors.initials: J
authors.lastname: Gensichen
authors.forename: Susanne
authors.initials: S
authors.lastname: Höfels
authors.forename: Heike
authors.initials: H
authors.lastname: Hansen
authors.forename: Hanna
authors.initials: H
authors.lastname: Leicht
authors.forename: Daniela
authors.initials: D
authors.lastname: Koller
authors.forename: Melanie
authors.initials: M
authors.lastname: Luppa
authors.forename: Anna
authors.initials: A
authors.lastname: Nützel
authors.forename: Jochen
authors.initials: J
authors.lastname: Werle
authors.forename: Martin
authors.initials: M
authors.lastname: Scherer
authors.forename: Karl
authors.initials: K
authors.lastname: Wegscheider
authors.forename: Gerd
authors.initials: G
authors.lastname: Glaeske
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schön
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care / Q000706:statistics & numerical data; D002908:Chronic Disease / Q000453:epidemiology*; D015897:Comorbidity; D003627:Data Interpretation, Statistical; D016208:Databases, Factual; D005260:Female; D015577:Geriatric Assessment / Q000379:methods*; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008297:Male; D015995:Prevalence; D011320:Primary Health Care / Q000706:statistics & numerical data; D018570:Risk Assessment; D012680:Sensitivity and Specificity