title: Methodological pitfalls in early detection studies - the NAPE Lecture 2002. Nordic Association for Psychiatric Epidemiology.
abstract: OBJECTIVE
  To identify and discuss methodological pitfalls that may help explain why many questions around early detection (ED) and duration of untreated psychosis (DUP) are still unsolved.
  
  
  METHODS
  This paper concentrates on pitfalls in the following areas: sampling, measurement and data analyses.
  
  
  RESULTS
  The main problems seem to be:
  
  
  METHODS
  Referral bias, exclusion of patients, patient refusal, and patients lost to follow-up.
  
  
  METHODS
  Reliability, which is particularly cogent for multisite investigations, and validity, which includes: Start of illness, start of psychosis, diagnoses, start of treatment, the relationship between ED and DUP and choice of outcome measures. Data Analyses: Overlooking threshold effects of DUP, improper control for baseline scores, and lack of control for confounders.
  
  
  CONCLUSIONS
  Methodological pitfalls may bias ED studies. Several pitfalls are unavoidable, but proper design and quality assurance can reduce their impact. Researchers ought to identify the pitfalls, and to estimate and discuss their influence.
authors.affiliation: Division of Psychiatry, Ullevål University Hospital, Oslo, Norway. svein.friis@psykiatri.uio.no
authors.forename: S
authors.initials: S
authors.lastname: Friis
authors.forename: T K
authors.initials: TK
authors.lastname: Larsen
authors.forename: I
authors.initials: I
authors.lastname: Melle
authors.forename: S
authors.initials: S
authors.lastname: Opjordsmoen
authors.forename: J O
authors.initials: JO
authors.lastname: Johannessen
authors.forename: U
authors.initials: U
authors.lastname: Haahr
authors.forename: E
authors.initials: E
authors.lastname: Simonsen
authors.forename: B R
authors.initials: BR
authors.lastname: Rund
authors.forename: P
authors.initials: P
authors.lastname: Vaglum
authors.forename: T
authors.initials: T
authors.lastname: McGlashan
mesh_terms: D006801:Humans; D008605:Mental Health Services / Q000592:standards*; D012017:Referral and Consultation; D015203:Reproducibility of Results; D012559:Schizophrenia / Q000175:diagnosis* / Q000628:therapy*; D013997:Time Factors; D016896:Treatment Outcome