title: Analysis of risk factors for schizophrenia with two different case definitions: a nationwide register-based external validation study.
abstract: Different case definitions of schizophrenia have been used in register based research. However, no previous study has externally validated two different case definitions of schizophrenia against a wide range of risk factors for schizophrenia. We investigated hazard ratios (HRs) for a wide range of risk factors for ICD-10 DCR schizophrenia using a nationwide Danish sample of 2,772,144 residents born in 1955-1997. We compared one contact only (OCO) (the case definition of schizophrenia used in Danish register based studies) with two or more contacts (TMC) (a case definition of at least 2 inpatient contacts with schizophrenia). During the follow-up, the OCO definition included 15,074 and the TMC 7562 cases; i.e. half as many. The TMC case definition appeared to select for a worse illness course. A wide range of risk factors were uniformly associated with both case definitions and only slightly higher risk estimates were found for the TMC definition. Choosing at least 2 inpatient contacts with schizophrenia (TMC) instead of the currently used case definition would result in almost similar risk estimates for many well-established risk factors. However, this would also introduce selection and include considerably fewer cases and reduce power of e.g. genetic studies based on register-diagnosed cases only.
authors.affiliation: Psychiatric Centre Copenhagen, Capital Region of Denmark, University Hospital of Copenhagen, Bispebjerg Bakke 23, 2400 NV, Denmark; The Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Denmark. Electronic address: holger.jelling.soerensen@regionh.dk.
authors.forename: Holger J
authors.initials: HJ
authors.lastname: Sørensen
authors.affiliation: National Centre for Register-based Research, Aarhus University, Business and Social Sciences, Aarhus, Denmark; The Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Denmark.
authors.forename: Janne T
authors.initials: JT
authors.lastname: Larsen
authors.affiliation: Research Department P, Aarhus University Hospital, Risskov, Denmark; The Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Denmark.
authors.forename: Ole
authors.initials: O
authors.lastname: Mors
authors.affiliation: Psychiatric Centre Copenhagen, Capital Region of Denmark, University Hospital of Copenhagen, Bispebjerg Bakke 23, 2400 NV, Denmark; The Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Denmark.
authors.forename: Merete
authors.initials: M
authors.lastname: Nordentoft
authors.affiliation: National Centre for Register-based Research, Aarhus University, Business and Social Sciences, Aarhus, Denmark; Centre for Integrated Register-based Research, CIRRAU, Aarhus University, Aarhus, Denmark; The Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Denmark.
authors.forename: Preben B
authors.initials: PB
authors.lastname: Mortensen
authors.affiliation: National Centre for Register-based Research, Aarhus University, Business and Social Sciences, Aarhus, Denmark; The Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Denmark.
authors.forename: Liselotte
authors.initials: L
authors.lastname: Petersen
mesh_terms: D000328:Adult; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007297:Inpatients; D008297:Male; D016016:Proportional Hazards Models; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D012559:Schizophrenia / Q000175:diagnosis* / Q000453:epidemiology* / Q000628:therapy; D012720:Severity of Illness Index; D012959:Socioeconomic Factors
keywords: Case definition; External validation; Register-based studies; Schizophrenia