title: Indirect calibration between clinical observers - application to the New York Heart Association functional classification system.
abstract: BACKGROUND
  Previous studies showed an inter-observer agreement for the NYHA classification of approximately 55%. The aim of this study was to calibrate the New York Heart Association (NYHA) classification system between observers, increasing its reliability.
  
  
  RESULTS
  Among 1136 community-dwellers in Porto, Portugal, aged ≥ 45 years, 265 reporting breathlessness answered a 4-item questionnaire to characterize symptom severity. The questionnaire was administered by 7 physicians who also classified the subject's functional capacity according to NYHA. Each subject was assessed by one physician. We calibrated NYHA classifications by the concurrent method, using 1-parameter logistic graded response model. Discrepancies between observers were assessed by differences in ability thresholds between NYHA classes I-II and II-III. The ability estimated by the model was used to predict the NYHA classification for each observer.Estimates of the first and second thresholds for each observer ranged from -1.92 to 0.46 and from 1.42 to 2.30, respectively. The agreement between estimated ability and the observers' NYHA classification was 88% (kappa = 0.61).
  
  
  CONCLUSIONS
  The study objectively indicates the main reason why several studies have reported low inter-observer is the existence of discrepant thresholds between observers in the definition of NYHA classes. The concurrent method can be used to minimize the reliability problem of NYHA classification.
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal. milton@med.up.pt.
authors.forename: Milton
authors.initials: M
authors.lastname: Severo
authors.forename: Rita
authors.initials: R
authors.lastname: Gaio
authors.forename: Patrícia
authors.initials: P
authors.lastname: Lourenço
authors.forename: Margarida
authors.initials: M
authors.lastname: Alvelos
authors.forename: Paulo
authors.initials: P
authors.lastname: Bettencourt
authors.forename: Ana
authors.initials: A
authors.lastname: Azevedo