Purpose: To evaluate the equivalence of electronic and paper versions of the Psoriasis Symptom Inventory and to examine measurement properties of the electronic version.
Methods: In a prospective, randomized, crossover, non-interventional study in adult subjects (age ≥18 years) with plaque psoriasis conducted over a period of 15 days, subjects were randomized to two groups, completing either the paper or electronic Psoriasis Symptom Inventory daily for 7 consecutive days followed by the alternate version. Equivalence was assessed by the intraclass correlation coefficient (ICC) between both administration modes. Differences in scores were also tested using paired Student's t test. Measurement properties included internal consistency reliability, test-retest reliability, and convergent and discriminant validity between the Psoriasis Symptom Inventory and (1) disease-specific (Dermatology Life Quality Index) and (2) general health (SF-36v2) status.
Results: Eighty subjects [74 % (59/80) moderate-to-severe psoriasis; 26 % (21/80) mild psoriasis receiving systemic treatment] were enrolled from 8 sites in the USA. The two modes were highly concordant for both total (ICC = 0.97) and individual item scores (ICC range = 0.93-0.97). Response bias testing showed no differences based on completion order with all ICC values >0.91. All mean score differences, except for one item ("flaking"), were non-significant (P > 0.05). Minimum values for reliability (>0.70) and validity (convergent, r ≥ 0.40) were exceeded for the electronic Psoriasis Symptom Inventory.
Conclusions: Equivalence between paper and electronic versions of the Psoriasis Symptom Inventory and strong measurement properties of the electronic mode indicated a successful migration from paper to electronic format of the Psoriasis Symptom Inventory.