Table 4 Contamination of intervention, adherence, and intervention credibility for the digital CBT-i and control groups

 Have you talked to your twin about the intervention you have received? n, Yes (%)

1 (6%)

3 (19%)

 Please indicate how confident you are that your twin did NOT know about the intervention you were receiving on a scale of 0 to 100, where 0 means “not at all” and 100 means “very confident”. Mean (SD)

86.7 (26.0)

85.5 (29.4)

 Were you aware of the intervention your twin was receiving? n, Yes (%)

1 (6%)

1 (6%)

 Did you change your behavior/attitude as a consequence of knowing about your twin intervention? n, Yes (%)

0 (0.00%)

0 (0.00%)

 0 sessions

2 (13%)

2 (6%)

 1 sessions

1 (6%)

9 (27%)

 2 sessions

2 (13%)

2 (6%)

 3 sessions

1 (6%)

2 (6%)

 4 sessions

0 (0%)

0 (0%)

 5 sessions

1 (6%)

3 (9%)

 6 sessions

9 (56%)

15 (46%)

 4–6 sessions

10 (63%)

18 (55%)

 How confident do you feel that this intervention can help you cope with your sleep problems?^a

3.75 (1.06)

2.80 (1.14)

0.95 (− 0.03–1.93)

3.17 (1.27)

2.18 (1.19)

0.99 (0.30–1.67)

 How confident do you feel that this intervention will help you manage your sleep problems?^a

3.92 (0.90)

2.42 (1.31)

1.50 (0.55–2.45)

3.29 (1.27)

2.04 (1.26)

1.26 (0.55–1.96)

 How confident would you be in recommending this intervention to a friend who suffered from similar complaints?^a

3.50 (1.00)

1.75 (1.48)

1.75 (0.68–2.82)

2.91 (1.56)

2.14 (1.30)

0.77 (0.03–1.58)

 How logical does this intervention seem to you?^a

4.18 (0.98)

3.83 (1.75)

0.35 (− 0.90–1.60)

3.96 (1.52)

2.39 (1.55)

1.57 (0.71–2.42)

 Total score (0–24)

15.31 (3.29)

10.69 (3.43)

4.61 (1.76–7.46)

13.38 (4.93)

8.75 (4.71)

4.62 (1.94–7.31)