title: Assessment of agreement in measuring orthodontic treatment need with the modified DHC.
abstract: OBJECTIVE
  To determine senior dental students' validity, reliability and category distinguishability when using the Dental Health Component (DHC) of the Index of Orthodontic Treatment Need (IOTN).
  
  
  METHODS
  Randomly selected pretreatment dental casts of 42 patients were used. The casts were assessed by six senior dental students after a 4-day training period and three orthodontists using the modified Dental Health Component (DHC) of the Index of Orthodontic Treatment Need (IOTN). Validity and reliability in assessing the DHC were measured using kappa and the category distinguishability with two modified association models: square scores association model and the agreement plus square scores association model.
  
  
  RESULTS
  The students' mean validity was 0.67 and their mean reliability was 0.65. For two students the better model was the square scores association-model (Categories 1 and 2: Mean 0.48; Categories 2 and 3: Mean 0.84). For four students the agreement plus square scores association model was the better model (Categories 1 and 2: Range: 0.90-0.99; Categories 2 and 3: 0.93-0.99)
  
  
  CONCLUSIONS
  In order to more precisely assess the reliability and validity of ordinal scales and the pattern of agreement between examiners association models should be used in addition to kappa.
authors.affiliation: Department of Biostatistics, Shahid Beheshti University, MC., Tehran, Iran. akbarzad@sbmu.ac.ir
authors.forename: Alireza Akbarzadeh
authors.initials: AA
authors.lastname: Bagheban
authors.forename: Mahtab
authors.initials: M
authors.lastname: Nourit
authors.forename: Mohammadreza
authors.initials: M
authors.lastname: Safavi
mesh_terms: D000293:Adolescent; D003753:Dental Health Surveys; D006801:Humans; D008310:Malocclusion / Q000175:diagnosis*; D003765:Models, Dental; D020380:Needs Assessment; D015588:Observer Variation; D009971:Orthodontics, Corrective; D015203:Reproducibility of Results; D013335:Students, Dental