title: Validation and internal consistency of Patient Health Questionnaire-9 for major depression in Parkinson's disease.
abstract: BACKGROUND
  depression is common in Parkinson's disease (PD), although frequently under-recognised. Among the scales used to investigate depressive features in PD, the Patient Health Questionnaire-9 (PHQ-9) has been largely used, but no specific cut-off scores for depression have been established thus far, which hinders the use of the PHQ-9 in clinical and research settings.
  
  
  OBJECTIVE
  we assessed the discriminant validity of the PHQ-9 in order to establish the best cut-off score for the diagnosis of major depression in PD patients.
  
  
  METHODS
  one hundred and ten patients with a diagnosis of PD without dementia were evaluated with the Structured Clinical Interview for DSM-IV (SCID), considered as the gold standard for the diagnosis of major depression. Eighty-four PD patients completed the PHQ-9, the 15-item Geriatric Depression Scale (GDS-15) and the Zung Self-rating Depression Scale (SDS).
  
  
  RESULTS
  the prevalence of current depression in the sample of PD patients was 25.5%. Maximal discrimination between depressed and non-depressed patients was reached with a cut-off score of 9 in the PHQ-9 (sensitivity of 100% and specificity of 83.1%). The internal consistency of the scale was 0.83 and, when used as a diagnostic instrument, the PHQ-9 had a sensitivity of 52.6% and specificity of 95.4%. The correlation coefficient between the PHQ-9 and the other two scales was 0.63.
  
  
  CONCLUSIONS
  the PHQ-9 is an adequate instrument for the screening-but not diagnosis-of depression in PD patients, with optimal sensitivity and specificity attained with a cut-off score of 9.
authors.affiliation: Behavior and Neurosciences Department, University of São Paulo, Av., Bandeirantes, 3900, Ribeirão Preto, SP 14048-900, Brazil. mchagas@fmrp.usp.br
authors.forename: Marcos Hortes N
authors.initials: MH
authors.lastname: Chagas
authors.forename: Vitor
authors.initials: V
authors.lastname: Tumas
authors.forename: Guilherme R
authors.initials: GR
authors.lastname: Rodrigues
authors.forename: João Paulo
authors.initials: JP
authors.lastname: Machado-de-Sousa
authors.forename: Alaor Santos
authors.initials: AS
authors.lastname: Filho
authors.forename: Jaime E C
authors.initials: JE
authors.lastname: Hallak
authors.forename: José Alexandre S
authors.initials: JA
authors.lastname: Crippa
mesh_terms: D000368:Aged; D000465:Algorithms; D001938:Brazil / Q000453:epidemiology; D016009:Chi-Square Distribution; D003865:Major Depressive Disorder / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D016002:Discriminant Analysis; D005260:Female; D006801:Humans; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D011237:Predictive Value of Tests; D015995:Prevalence; D011569:Psychiatric Status Rating Scales; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires
keywords: PHQ-9; Parkinson's disease; major depression; older people; psychiatric status rating scale