title: The internal and external validity of the Major Depression Inventory in measuring severity of depressive states.
abstract: BACKGROUND
  We have developed the Major Depression Inventory (MDI), consisting of 10 items, covering the DSM-IV as well as the ICD-10 symptoms of depressive illness. We aimed to evaluate this as a scale measuring severity of depressive states with reference to both internal and external validity.
  
  
  METHODS
  Patients representing the score range from no depression to marked depression on the Hamilton Depression Scale (HAM-D) completed the MDI. Both classical and modern psychometric methods were applied for the evaluation of validity, including the Rasch analysis.
  
  
  RESULTS
  In total, 91 patients were included. The results showed that the MDI had an adequate internal validity in being a unidimensional scale (the total score an appropriate or sufficient statistic). The external validity of the MDI was also confirmed as the total score of the MDI correlated significantly with the HAM-D (Pearson's coefficient 0.86, P < or = 0.01, Spearman 0.80, P < or = 0.01).
  
  
  CONCLUSIONS
  When used in a sample of patients with different states of depression the MDI has an adequate internal and external validity.
authors.affiliation: Psychiatric Research Unit, Frederiksborg General Hospital, Hillerød, Denmark.
authors.forename: L R
authors.initials: LR
authors.lastname: Olsen
authors.forename: D V
authors.initials: DV
authors.lastname: Jensen
authors.forename: V
authors.initials: V
authors.lastname: Noerholm
authors.forename: K
authors.initials: K
authors.lastname: Martiny
authors.forename: P
authors.initials: P
authors.lastname: Bech
mesh_terms: D000328:Adult; D003865:Major Depressive Disorder / Q000175:diagnosis*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires