title: Variability in clinical diagnoses during the ICD-8 and ICD-10 era.
abstract: To explore whether the diagnostic homogeneity in a daily, routine clinical activity changed visibly over two historical periods (the ICD-8 and the ICD-10 era) across and within five psychiatric in-patient clinics.
  
  
  
  In this register study, we analyzed the discharge diagnoses from five university-affiliated departments of psychiatry in Denmark in two time periods: 1980-1985 (ICD-8) and 2001-2010 (ICD-10).
  
  
  
  The synchronic inter-departmental diagnostic differences did not decrease in the ICD-10 era compared with ICD-8 era. Nor did the diachronic stability within each department become more homogeneous.
  
  
  
  The diagnostic variability reflected by the diagnostic differences between the departments and by the diagnostic homogeneity within each department remained similar in the two historical periods with no evidence of an increased homogeneity of diagnostic habits after the introduction of the ICD-10.
  
  
  
  There is a myriad of variables that affects the diagnostic variability over time that we were not able to control.
authors.affiliation: Early Psychosis Intervention Center, Region Zealand, University of Copenhagen, Smedegade 16, 4000, Roskilde, Denmark. juef@regionsjaelland.dk.
authors.forename: Julie
authors.initials: J
authors.lastname: Nordgaard
authors.affiliation: Center for Clinical Intervention and Neuropsychiatric Schizophrenia Research and Center for Neuropsychiatric Schizophrenia Research, Mental Health Center Glostrup, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Kasper
authors.initials: K
authors.lastname: Jessen
authors.affiliation: Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, University of Copenhagen, The Capital Region, Copenhagen, Denmark.
authors.forename: Ditte
authors.initials: D
authors.lastname: Sæbye
authors.affiliation: Center for Subjectivity Research, University of Copenhagen, Copenhagen, Denmark.|Mental Health Centre Hvidovre, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Josef
authors.initials: J
authors.lastname: Parnas
mesh_terms: D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology; D003718:Denmark / Q000453:epidemiology; D003866:Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology; D006760:Hospitalization; D006801:Humans; D007297:Inpatients / Q000706:statistics & numerical data*; D038801:International Classification of Diseases; D001523:Mental Disorders / Q000175:diagnosis / Q000453:epidemiology*; D010554:Personality Disorders / Q000175:diagnosis / Q000453:epidemiology; D011158:Population Growth; D011570:Psychiatry; D012042:Registries; D015203:Reproducibility of Results; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology; D012569:Schizotypal Personality Disorder / Q000175:diagnosis / Q000453:epidemiology
keywords: Clinical; Diagnosis; ICD-10; ICD-8; Uniformity