Direction of wording and responses to items in oral health-related quality of life questionnaires for children and their parents.

OBJECTIVES: In order to minimize acquiescence response set bias, it is often recommended that questionnaires measuring attitudes, behaviours or health states contain items worded positively and negatively. It has also been suggested that when measuring health status this approach means that both the negative and positive dimensions of health can be assessed. This study aimed at assessing the performance of negatively and positively worded items in questionnaires to measure child and parent perceptions of child oral health-related quality of life.
METHODS: Both the child and parent questionnaire included four pairs of items, one negatively worded and one positively worded, that assessed eating, appearance, oral self-care and self-confidence. The response format was a five-point Likert frequency scale with a 'Don't know' option. Prior to analysis, the positive items were reverse coded. The relative performance of the two sets of items was assessed by means of comparisons of the proportions with 'Don't know' responses or missing values, mean item scores and proportions with the two highest frequency codes. Kappa statistics and intraclass correlation coefficients were used to assess the agreement between the negative and reverse-coded positive items and scores and the agreement between child and parent pairs. Factor analysis was used to determine if the two sets of items were measuring the same underlying construct.
RESULTS: The study was completed by 91 Canadian children and 100 parents (91 child-parent pairs) recruited from clinics treating paediatric, orthodontic and oro-facial conditions. The positively worded items elicited substantially more 'Don't know' responses or missing values than the negatively worded items and failed to discriminate between groups. In addition, mean item scores and proportions with the highest frequency codes were substantially larger for reverse-coded positive than negative items. Agreement between pairs of items was slight. Child-parent agreement was substantial for a scale constructed from the negative items but only moderate for the positive items. Factor analysis revealed that the two sets of items loaded onto different factors.
CONCLUSIONS: The performance of the positively worded items was unsatisfactory and their use in oral health-related quality of life indexes, either to reduce response set or assess positive oral health, is at best questionable.