title: Mania in the Swedish Twin Registry: criterion validity and prevalence.
abstract: BACKGROUND
  In population surveys, the assessment of mania is commonly done by trained lay interviewers using structured diagnostic instruments: the validity of this approach has been questioned. We examined the criterion validity and prevalence of lifetime mania in a survey of Swedish twins conducted with interview methodology usually applied in psychiatric epidemiology.
  
  
  METHODS
  41 838 individuals in the Swedish Twin Registry were evaluated via a telephone interview that included the eight DSM-IV mania items, and these data were merged with inpatient hospitalization discharge diagnoses from two comprehensive national registries (the criterion). An algorithm with eight cut-points was used to diagnose lifetime mania, and compared by a receiver operator characteristic curve to the criterion. The algorithm requiring at least four positive items resembling a DSM-IV diagnosis.
  
  
  RESULTS
  History of hospitalization for a psychiatric condition that included a manic episode was present for 0.7% of all living twins, and predicted non-response to the survey (OR = 0.5; 95% CI = 0.4-0.6). The incidence rate for first hospitalization was 2.1/10 000 year(-1). For > or =1 symptom (first cut-point), the prevalence, sensitivity and specificity were 3.6%, 39.0% and 96.6%; for > or = 4 symptoms (DSM-IV-like cut-point) 2.6%, 36.5% and 97.6%; and for eight symptoms 0.3%, 18.0% and 99.8%. Positive predictive values were, respectively, 5.5%, 7.0% and 29.8%.
  
  
  CONCLUSIONS
  The performance of the telephone screening for mania by lay interviewers in terms of positive predictive power was not satisfactory; despite a high specificity, the false positive rate was high. The low population prevalence of mania, non-response bias, criterion choice and inherent limitations of the interviewing method are among the explanations. Assessment of a lifetime manic episode based on lay interviewer screening may yield misleading data.
authors.affiliation: Department of Psychiatry, Harvard University, Boston, MA, USA
authors.forename: Federico
authors.initials: F
authors.lastname: Soldani
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Sullivan
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
mesh_terms: D001714:Bipolar Disorder / Q000453:epidemiology / Q000208:ethnology*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D011159:Population Surveillance; D015995:Prevalence; D012042:Registries; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D014427:Twins / Q000208:ethnology*