Assessment of agreement in measuring orthodontic treatment need with the modified DHC.

AIMS: 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)

CONCLUSION: 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.