The reliability, validity, and preliminary responsiveness of the Eye Allergy Patient Impact Questionnaire (EAPIQ)

BACKGROUND: The Eye Allergy Patient Impact Questionnaire (EAPIQ) was developed based on a pilot study conducted in the US and focus groups with eye allergy sufferers in Europe. The purpose of this study was to present the results of the psychometric validation of the EAPIQ. METHODS: One hundred forty six patients from two allergy clinics completed the EAPIQ twice over a two-week period during the fall and winter allergy seasons, along with concurrent measures of health status, work productivity, and utility. Construct validity, reliability (internal consistency and test-retest), concurrent, known-group, and clinical validities, and responsiveness of the EAPIQ were assessed. Known-group validity was assessed by comparing EAPIQ scale scores between patients grouped according to their self-rating of ocular allergy severity (no symptoms, very mild, mild, moderate, severe, very severe). Clinical validity was assessed by assessing differences in EAPIQ scores between groups of patients rated by their clinician as non-symptomatic, mild, moderate, and severe. RESULTS AND DISCUSSION: Results from the validation study suggested the deletion of 14 of 43 items (including embedded questions) that required patients to complete the percentage of time they were troubled by something (daily activity limitations/emotional troubles). These items yielded a significant amount of missing or inconsistent data (50%). The resulting factor analysis suggested four domains: symptoms, daily life impact, psychosocial impact, and treatment satisfaction. When included as separate scales, the symptom-bother and symptom-frequency scales were highly correlated (> 0.9). As a consequence, and due to superior discriminative validity, the symptom bother and frequency items were summed. All items met the tests for item convergent validity (item-scale correlation = 0.4). The success rate for item discriminant validity testing was 97% (item-scale correlation greater with own scale than with any other). The criterion for internal consistency reliability (alpha coefficient ≥ 0.70) was met for all EAPIQ scales (range 0.89–0.93), as was the criterion for test-retest reliability (intraclass correlation [ICC] ≥ 0.70). Largely moderate correlations between the scales of the EAPIQ and the mini Rhinoconjunctivitis Quality of Life Questionnaire (miniRQLQ) and low correlations with the Health Utilities Index 2/3 (HUI2/3) were indicative of satisfactory concurrent validity. The EAPIQ symptoms, Daily Life Impact, and Psychosocial Impact scales were able to distinguish between patients differing in eye allergy symptom severity, as rated by patients and clinicians, providing evidence of satisfactory known-group and clinical validities, respectively. Preliminary analyses indicated the EAPIQ Symptoms, Daily Life Impact, and Psychosocial Impact scales to be responsive to changes in eye allergies. CONCLUSION: Following item reduction, construct validity, reliability, concurrent validity, known-group validity, and preliminary responsiveness were satisfactory for the EAPIQ in this population of ocular allergy patients.