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Table 4 Reliability, floor, ceiling effect, and measurement error of the Insomnia Severity Index Danish version (n = 163)

From: Preliminary validation of the insomnia severity index in Danish outpatients with a medical condition

Floor effects, n [%] 11 [4.4]
Ceiling effects, n [%] 0 [0.0]
Reliability
 Internal consistency, Cronbach’s alpha [inter-item correlation range]
  Global scale (all 7 scale items) 0.90 [0.52–0.80]
  Model 2
   Severity subscale (item 1, 2, 3, 4) 0.83 [0.74–0.88]
   Impact subscale (item 5, 6, 7) 0.88 [0.85–0.92]
  Model 4
   Severity subscale (item 1, 2, 3) 0.75 [0.38–0.55]
   Dissatisfaction subscale (item 1, 4, 7) 0.81 [0.50–.072]
   Impact subscale (item 5, 6, 7) 0.88 [0.63–0.79]
 Test-retest reliability
  ICC [95%CI] 0.90 [0.87–0.93]
Measurement error
 SEM (\( \sqrt{mean} square(ANOVA) \)) 2.52
 SDC (1.96 ×  √ 2 × SEM) 6.99
 LoA (mean difference between test and retest) [95% limits] 0.05 [−6.92–7.02]
  1. ICC Intraclass correlation, CI confidence interval, SEM standard error of measurement, SDC smallest detectable change, LoA limits of agreement