Assessing health-related quality of life in hand eczema patients: how to overcome psychometric faults when using the dermatology life quality index.

Health-related quality of life (HRQOL) has become an important patient reported outcome in health service research. The dermatology life quality index (DLQI) is the most commonly used instrument in dermatology. In recent years, the psychometric properties of the DLQI have been a subject of debate as requirements of modern test theory seem not to be fulfilled. The aim of this study was to test whether those violations also occur in patients with hand eczema. We collected data of 602 hand eczema patients who participated in an inpatient dermatology rehabilitation program in Germany. In order to report meaningful scores of the DLQI, data were analysed according to the principles of modern test theory. We calibrated the DLQI using the Rasch model, resulting in a 6 item version with a range between 0-15 points. This version showed no significant misfit to the Rasch model (p>0.14). By using a Rasch analysis the results were evaluated in a second sample of hand eczema patients (n=511). Even if all demographic characteristic of this sample were different, we were able to replicate the results found in this study (p>0.21). In conclusion, we recommend to use an alternative scoring procedure as presented in this article if the DLQI is used in hand eczema patients.