Measuring severity of psoriasis: methodological issues

Abstract

A validated measure of psoriatic severity is needed for effective treatment and research of the disease. The absence of such a measure has led many investigators to create their own methods of assessing psoriasis, while many others use such popular measurement techniques as the psoriasis area and severity index (PASI). Though few studies have been conducted to investigate the accuracy and usefulness of the PASI, investigators worldwide continue to use it in the evaluation of treatment. Investigators in the psychological sciences use an established set of measurement criteria (referred to as psychometrics) to evaluate and modify scales that measure psychological constructs. However, these same criteria also can be utilized in determining how well the PASI, as well as the various other methods of psoriatic assessment, measure severity. In this paper, the scale of properties of validity and reliability are discussed, including a review of the research addressing these properties within the PASI. Finally, a discussion of the future research needed in the assessment of psoriasis is provided.

Key Words:

• Validity
• Reliability
• PASI