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Item reduction and psychometric validation of the Oily Skin Self Assessment Scale (OSSAS) and the Oily Skin Impact Scale (OSIS).

INTRODUCTION
Developed using focus groups, the Oily Skin Self Assessment Scale (OSSAS) and Oily Skin Impact Scale (OSIS) are patient-reported outcome measures of oily facial skin.


OBJECTIVE
The aim of this study was to finalize the item-scale structure of the instruments and perform psychometric validation in adults with self-reported oily facial skin.


METHODS
The OSSAS and OSIS were administered to 202 adult subjects with oily facial skin in the United States. A subgroup of 152 subjects returned, 4 to 10 days later, for test–retest reliability evaluation.


RESULTS
Of the 202 participants, 72.8% were female; 64.4% had self-reported nonsevere acne. Item reduction resulted in a 14-item OSSAS with Sensation (five items), Tactile (four items) and Visual (four items) domains, a single blotting item, and an overall oiliness item. The OSIS was reduced to two three-item domains assessing Annoyance and Self-Image. Confirmatory factor analysis supported the construct validity of the final item-scale structures. The OSSAS and OSIS scales had acceptable item convergent validity (item-scale correlations >0.40) and floor and ceiling effects (<20%). Cronbach's alpha coefficients ranged from 0.83 to 0.89 for the OSSAS and 0.82 to 0.87 for the OSIS, demonstrating excellent internal consistency. The a priori test–retest reliability criterion (intraclass correlation [ICC] ≥0.7) was met for one of the three OSSAS domains and one of the two OSIS domains. OSSAS and OSIS domains distinguished among groups that differed in patient-reported facial oily skin severity (P < 0.0001), and bother associated with oily skin (P < 0.0001).


CONCLUSIONS
The OSSAS and OSIS versions tested in this study have been found to have strong psychometric properties in this patient sample (adults with self-reported oily facial skin), as assessments of self-reported oily facial skin severity and its emotional impact, respectively.