Rasch Analysis of the Dermatology Life Quality Index in Turkish Psoriasis Patients: Validation Study

Abstract

Objective: The Dermatology Life Quality Index (DLQI) is a widely used quality of life scale in many dermatological diseases such as psoriasis. Recently, there have been discussions about the inadequacy of DLQI in the evaluation of dermatological diseases. This study aimed to examine the psychometric properties of the DLQI scale, in a sample of Turkish psoriatic patients. Material and Methods: A total of 979 psoriasis patients, 509 male (52.4%) and 470 female (47.6%), who filled out the DLQI questionnaire between April 2013 and January 2019, were included in the study. This was a retrospective study conducted. Data were analyzed using the Rasch model to obtain meaningful scores for the DLQI. Results: According to the Rasch analysis, the measurement ability of the ninth question was found to be insufficient in general. It has been determined that DLQI scale items can vary in measuring ability according to age, gender and marital status are insufficient. In addition, it was found that the assumption that the answers in Likert-type expressions in the DLQI scale are equidistant from each other is not correct. Conclusion: DLQI seems to have a poor fit with the Rasch model for Turkish psoriasis patients. In addition, DLQI may vary according to age, gender and marital status. Therefore, it is recommended to develop new scales in the evaluation of psoriasis patients.