Health-related quality-of-life is typically measured using disease-specific or generic measures, and both types may be used together in order to address both clinical and broader policy questions, and to detect unexpected differences [1
]. Disease-specific measures are used when disease-related attributes need to be assessed and greater sensitivity to the clinical condition under consideration is required. Generic measures are used when the relevant variables are covered and when comparisons between different diseases are required.
The Oral Health Impact Profile (OHIP) measures people's perceptions of the social impact of oral disorders on their well-being [2
]. The OHIP-49 contains 49 questions that capture seven conceptually formulated dimensions based on Locker's theoretical model of oral health [3
] adapted from the WHO framework used to classify impairments, disabilities and handicaps [4
], and the OHIP-14 was developed as a shorter version of the OHIP for settings where the full battery of 49 questions is inappropriate [5
The EuroQol was developed as a standardised non-disease-specific instrument for describing and valuing health-related quality of life [6
]. The EuroQol is intended to complement other forms of quality of life measures and it was purposefully developed to generate a generic index of health. Any classified health state can be valued using preferences elicited from a general population [6
], and values can be modelled from such data sets [7
]. The EuroQol is widely used internationally and reported to have adequate construct and convergent validity, but is highly skewed and has relatively poor sensitivity especially in relation to disease-based outcomes research [1
In comparing generic and disease-specific measures it has been noted that possible explanations for the disease-specific measures being more sensitive to change could relate to the fact that patients perceive assessments of overall health as independent from condition-specific assessments which tend to focus on symptoms of the condition [8
]. It has also been noted that disease-specific instruments may focus too narrowly on symptoms so that they fail to capture some broader domains included in generic instruments. It has also been suggested that even some generic instruments may not overlap but represent different domains of knowledge [9
]. Oral health-related quality of life has been compared using specific and generic instruments. For example, a comparison between conventional and implant denture patients showed that the specific measure of oral health (OHIP-20) was better in the implant group but no significant differences between patient groups were found in the generic measure (SF-36) that was used [10
]. Other studies have also concluded that oral specific measures such as OHIP will be of greater use in measuring outcomes of oral disorders than generic measures such as SF-36 because the majority of the SF-36 domains are not sensitive to changes in oral health and exhibit limited construct validity [11
]. However, despite being a generic measure the EuroQol has shown discriminant validity in relation to a range of dental patient, visit and oral health measures [12
]. The aims of this study were to compare the dimensions of oral-health-related quality-of-life measured by a generic health state measure, the EuroQol, and a specific oral health measure, the OHIP. By comparing the dimensions of these measures we aim to obtain a clearer picture of what they are measuring, which has application in determining whether one instrument can be interchanged with the other (if they measure the same thing), or if there is justification in using both (if they measure different things). The EuroQol could be useful in terms of efficiently broadening the domains measured if it did not overlap with OHIP.