Table 3.

Discriminative validity of the Insomnia Severity Index Danish version (ISI-DK)

Hypotheses	Mean ISI-DK score (SD)
Gender: Female responders have significantly higher ISI-DK mean scores compared to male responders
Male, n = 91	9.36 (6.03)
Female, n = 158	10.74 (6.02)
Effect size (Cohen’s d)	0.23
p-value	0.083
Confirmed hypothesis	No
Age: Responders ≥ 70 years old have significantly lower ISI-DK mean scores compared to younger responders
≥ 70, n = 60	8.85 (6.55)
≤ 69, n = 188	10.65 (5.83)
Effect size (Cohen’s d)	0.40
p-value	0.044
Confirmed hypothesis	Yes
EQ VAS: Responders with EQ VAS score < 83.7 have significantly higher ISI-DK mean scores compared to responders with higher EQ VAS scores
VAS score ≤ 83.6, n = 189	11.21 (6.00)
VAS score ≥ 83.7, n = 60	7.18 (5.13)
Effect size (Cohen’s d)	0.69
p-value	< 0.001
Confirmed hypothesis	Yes
EQ-5D anxiety/depression: Responders with any EQ-5D anxiety/depression problem have significantly higher ISI-DK mean scores compared to responders with no problem
Anxiety/depression no problems, n = 132	8.23 (5.66)
Anxiety/depression problems, n = 117	12.50 (5.68)
Effect size (Cohen’s d)	0.75
p-value	< 0.001
Confirmed hypothesis	Yes
EQ-5D pain/discomfort: Responders with any EQ-5D pain/discomfort problem have significantly higher ISI-DK mean scores compared to responders with no problem
Pain/discomfort no problems, n = 64	7.44 (5.28)
Pain/discomfort problems, n = 185	11.21 (6.01)
Effect size (Cohen’s d)	0.65
p-value	< 0.001
Confirmed hypothesis	Yes

Cut-off for effect size: 0.2 (small), 0.5 (medium) and 0.8 (large)