Categorization of Skindex-29 scores using mixture analysis

Background: Although the Skindex-29 is among the most commonly used health-related quality of life instruments in dermatology, the interpretation of obtained scores is not well documented. Objective: To create categories of the scores of the Skindex-29. Methods: The Skindex-29 scores of454 Italian patients with 6 distinct skin diseases from a specialized center were analyzed using mixture analyses. The validity of the obtained categorizations was tested. Results: Mixture analysis showed 4 distinct components (categories) for the emotion and functioning scale and 5 for the symptom scale. The total Skindex-29 score was categorized into 4 levels. As expected, patients with inflammatory diseases had higher levels of impairment, those with vitiligo and alopecia areata had low symptom levels and those with nevi were predominantly located in the lower categories for each of the scales. Conclusion: The proposed categories of the Skindex-29 may ease the interpretation of obtained continuous scores.