Assessing the responsiveness of measures of oral health-related quality of life.

OBJECTIVES: This paper illustrates ways of assessing the responsiveness of measures of oral health-related quality of life (OHRQoL) by examining the sensitivity of the oral health impact profile (OHIP)-14 to change when used to evaluate a dental care program for the elderly.
METHODS: One hundred and sixteen elderly patients attending four municipally funded dental clinics completed a copy of the OHIP-14 prior to treatment and 1 month after the completion of treatment. The post-treatment questionnaire also included a global transition judgement that assessed subjects' perceptions of change in their oral health following treatment at the clinics. Change scores were calculated by subtracting post-treatment OHIP-14 scores from pre-treatment scores. The longitudinal construct validity of these change scores were assessed by means of their association with the global transition judgements. Measures of responsiveness included effect sizes for the change scores, the minimal important difference, and Guyatt's responsiveness index. An receiver operating characteristic (ROC) curve was constructed to determine the accuracy of the change scores in predicting whether patients had improved or not as a result of the treatment.
RESULTS: Based on the global transition judgements, 60.2% of subjects reported improved oral health, 33.6% reported no change, and only 6.2% reported that it was a little worse. These changes are reflected in mean pre- and post-treatment OHIP-14 scores that declined from 15.8 to 11.5 (P < 0.001). Mean change scores showed a consistent gradient in the expected direction across categories of the global transition judgement, but differences between the groups were not significant. However, paired t-tests showed no significant differences in the pre- and post-treatment scores of stable subjects, but showed significant declines for subjects who reported improvement. Analysis of data from stable subjects indicated that OHIP-14 had excellent test-retest reliability with an intraclass correlation coefficient (ICC) of 0.84. Effect size based on change scores for all subjects and subgroups of subjects were small to moderate. The ROC analysis indicated that OHIP-14 change scores were not good "diagnostic tests" of improvement. The minimal important difference for the OHIP-14 was of 5-scale points, but detecting this difference would require relatively large sample sizes.
CONCLUSIONS: OHIP-14 appeared to be responsive to change. However, the magnitude of change that it detected in the context described here was modest, probably because it was designed primarily as a discriminative measure. The psychometric properties of the global transition judgements that often provide the "gold standard" for responsiveness studies need to be established. Copyright Blackwell Munksgaard, 2004