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Table 2 Internal consistency (Cronbach's alpha) and test-retest reliability (Intraclass Correlation Coefficients, ICC) properties of the IDEEL

From: Development and validation of the impact of dry eye on everyday life (IDEEL) questionnaire, a patient-reported outcomes (PRO) measure for the assessment of the burden of dry eye on patients

Dimensions of the IDEEL Cronbach's α coefficient (N*) ICC
(N**)
Dry Eye Symptom-Bother module*   
Dry eye Symptom Bother 0.97 (209) 0.88 (167)
Dry Eye Impact module*   
Impact on Daily Activities 0.86 (209) 0.77 (167)
Emotional Impact due to Dry Eye 0.94 (209) 0.83 (167)
Impact on Work Scale 0.86 (128) 0.70 (106)
Dry Eye Treatment Satisfaction module*   
Satisfaction with Treatment Effectiveness 0.87 (125) 0.70 (111)
Treatment-related Bother/Inconvenience 0.70 (139) 0.80 (130)
  1. * Number of patients who completed more than half of the items in the respective dimensions
  2. ** Number of patients for whom a score could be calculated and who were stable between the 2 visits according to the Dry Eye Change Scale (N = 167)