Validation of the electronic Psoriasis Area and Severity Index application : Establishing measurement equivalence

To the Editor: Despite its many shortcomings, the Psoriasis Area and Severity Index (PASI) remains the standard method worldwide for psoriasis assessment.1 Several studies have implemented electronic versions without evidence of formal validation, raising the possibility of lack of equivalence with the paper counterpart.2 This study compared the conventional paper-based and a novel electronic application version of the PASI (Fig 1). International Society for Pharmacoeconomics and Outcomes Research (ISPOR) guidelines3 were followed to assess rater preference and consistency of scores.