Demonstrating measurement equivalence of the electronic and paper formats of the Urticaria Patient Daily Diary in patients with chronic idiopathic urticaria.

Background: The Urticaria Patient Daily Diary (UPDD), originally developed on paper, is a measure of key symptoms of chronic idiopathic urticaria (CIU). The development of the electronic version (eUPDD) involved moderate modifications to the appearance of the paper version.

Objective: This study assessed the measurement equivalence of the electronic and paper versions of the UPDD in a sample of patients with CIU.

Methods: This was a cross-over study of patients with moderate-severe CIU refractory to H1 antihistamines. Patients were randomized to either the eUPDD followed by the paper UPDD or vice versa. The UPDD includes morning and evening questions; both sets were administered together in this study. An hour-long filler task was given between paper and electronic administrations. Patients with stable symptoms between the two assessments were included in the analyses. Cohen's kappa coefficients and intraclass correlation coefficients (ICC) were computed as applicable to assess equivalence.

Results: A total of 91 patients participated (mean age 43 years, 79.1 % female). Symptoms were stable between assessments for 67-74 (74-81 %) patients (varied by symptom). Kappa coefficients ranged from 0.82 to 1.00 for the individual UPDD items. For the Urticaria Activity Score (the sum of the 'itch severity' and 'number of hives' item scores) the ICC was 0.90 for the morning (Wilcoxon p = 0.331) and 0.95 for the evening (Wilcoxon p = 0.836).

Conclusions: All test-retest statistics in this study were well above the accepted threshold, indicating excellent agreement between the two administration methods. Findings support the measurement equivalence of the electronic and paper versions of the UPDD to measure CIU symptoms.