Impact of response shift on the assessment of treatment effects using the Oral Health Impact Profile

The assessment of changes in oral health-related quality of life (OHRQoL) is challenging because individuals' concepts and internal standards of OHRQoL may change over time. The aim of this study was to detect response shifts in OHRQoL assessments made using the Oral Health Impact Profile (OHIP). Oral health-related quality of life was assessed in a consecutive sample of 126 patients seeking prosthodontic care. Patients were asked to rate their OHRQoL before treatment started and 1 month after treatment was finished, using the German 49-item version of the OHIP. When rating their OHRQoL after treatment, patients were also asked to rate their pre-treatment OHRQoL without having access to their baseline data. The response shift was calculated as the difference in OHIP summary scores between the initial assessment and the retrospective baseline assessment. The OHIP mean scores decreased from 31.8 at the initial baseline assessment to 24.4 after treatment. The retrospective baseline assessment resulted in an OHIP mean score of 38.1, corresponding to a response shift of 6.3 OHIP points. The effect size (Cohen's d = 0.21) of the response shift was considered small. The response shift phenomenon and its magnitude have important implications for dental practice, where patients and dentists often assess perceived treatment effects retrospectively.