Objectives: This study examined parental knowledge of their children's oral-health-related quality of life (OHRQoL) (Objective 1), and the effects of different analytical techniques to manage 'Don't know' (DK) responses on the validity and reliability of the questionnaire (Objective 2) and the level of agreement between parental and child reports (Objective 3).
Methods: The parental (PPQ) and child (CPQ11-14) components of the Child Oral Health Quality of Life Questionnaire were used. Objectives 1 and 2 were addressed in the study that involved 221 parents and Objective 3 in the study that involved 63 pairs of parents and children. Four methods for treating DK responses in the PPQ were tested: listwise deletion, item mean imputation, imputation of the value zero and adjustment of scores to account for items with DK responses.
Results: Respectively, 26 and 11% of the parents gave > or = 3 and 6 > or = DK responses to 33 items comprising the PPQ. DK responses were associated with child's age and clinical condition, and parental gender. The methods of managing DK responses did not have differing effects on the measurement properties of the PPQ and the level of agreement between parents and children.
Conclusion: Some parents have limited knowledge concerning their children's OHRQoL. However, given that parental and child reports are measuring different realities, information provided by parents is useful even if it is incomplete.