Evaluation of psychometric properties and differential item functioning of 8-item Child Perceptions Questionnaires using item response theory

Background Four-factor structure of the two 8-item short forms of Child Perceptions Questionnaire CPQ11–14 (RSF:8 and ISF:8) has been confirmed. However, the sum scores are typically reported in practice as a proxy of Oral health-related Quality of Life (OHRQoL), which implied a unidimensional structure. This study first assessed the unidimensionality of 8-item short forms of CPQ11–14. Item response theory (IRT) was employed to offer an alternative and complementary approach of validation and to overcome the limitations of classical test theory assumptions.