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Table 6 Internal consistency reliability symptom subscale (items 1, 2, 4, 5, 8, 9, 10 and 11) score at Days 1, 4, and 8 (Cronbach’s Alpha)

From: Patient-reported outcomes to assess the efficacy of extended-release guaifenesin for the treatment of acute respiratory tract infection symptoms

    Item Cronbach’s alpha Cronbach’s alpha with item deleted
  Day 1 Day 4 Day 8 Day 1 Day 4 Day 8
Subscale score alpha 0.76 0.87 0.90    
  (n = 310) (n = 305) (n = 290)    
1. Bring up phlegm     0.73 0.84 0.88
2. Difficult to breathe     0.72 0.84 0.88
4. Annoyed by phlegm     0.71 0.83 0.87
5. Interference with ability to speak     0.71 0.84 0.88
8. Phlegm thickness     0.72 0.85 0.88
9. Difficulty bringing up phlegm     0.81 0.90 0.93
10. Cough when woke up     0.73 0.84 0.88
11. Cough during day     0.74 0.84 0.88