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Randomized Controlled Trial
. 2021 Oct 11;44(10):zsab118.
doi: 10.1093/sleep/zsab118.

The effect of sleep-wake intraindividual variability in digital cognitive behavioral therapy for insomnia: a mediation analysis of a large-scale RCT

Cecilie L Vestergaard  1   2 , Øystein Vedaa  1   2   3   4 , Melanie R Simpson  5   6 , Patrick Faaland  1   2 , Daniel Vethe  1   2 , Kaia Kjørstad  1   2 , Knut Langsrud  2 , Lee M Ritterband  7 , Børge Sivertsen  1   3   8 , Tore C Stiles  9 , Jan Scott  1   10 , Håvard Kallestad  1   2
Affiliations
Randomized Controlled Trial

The effect of sleep-wake intraindividual variability in digital cognitive behavioral therapy for insomnia: a mediation analysis of a large-scale RCT

Cecilie L Vestergaard et al. Sleep. .

Abstract

Study objectives: Digital cognitive behavioral therapy for insomnia (dCBT-I) is an effective treatment for insomnia. However, less is known about mediators of its benefits. The aim of the present study was to test if intraindividual variability in sleep (IIV) was reduced with dCBT-I, and whether any identified reduction was a mediator of dCBT-I on insomnia severity and psychological distress.

Methods: In a two-arm randomized controlled trial (RCT), 1720 adults with insomnia (dCBT-I = 867; patient education about sleep = 853) completed the Insomnia Severity Index (ISI), the Hospital Anxiety and Depression Scale (HADS) and sleep diaries, at baseline and 9-week follow-up. Changes in IIV were analyzed using linear mixed modeling followed by mediation analyses of ISI, HADS, and IIV in singular sleep metrics and composite measures (behavioral indices (BI-Z) and sleep disturbance indices (SI-Z)).

Results: dCBT-I was associated with reduced IIV across all singular sleep metrics, with the largest between-group effect sizes observed for sleep onset latency (SOL). Reduced IIV for SOL and wake after sleep onset had the overall greatest singular mediating effect. For composite measures, SI-Z mediated change in ISI (b = -0.74; 95% confidence interval (CI) -1.04 to -0.52; 13.3%) and HADS (b = -0.40; 95% CI -0.73 to -0.18; 29.2%), while BI-Z mediated minor changes.

Conclusion: Reductions in IIV in key sleep metrics mediate significant changes in insomnia severity and especially psychological distress when using dCBT-I. These findings offer important evidence regarding the therapeutic action of dCBT-I and may guide the future development of this intervention.

Clinical trials: Name: Overcoming Insomnia: Impact on Sleep, Health and Work of Online CBT-I Registration number: NCT02558647 URL: https://clinicaltrials.gov/ct2/show/NCT02558647?cond=NCT02558647&draw=2&rank=1.

Keywords: CBT-I; intraindividual variability; mediation analysis; randomized controlled trial; sleep–wake cycle.

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Figures

Figure 1.
Figure 1.
Mediation model with composite scores as mediators and Insomnia Severity Index (ISI) as outcome. Values represent unstandardized regression coefficients. Values in parentheses represent estimations of 95% confidence intervals. Values with percentage represent the estimated percentage mediated effect. Covariates: sex, age, baseline values of ISI, BI-Z, and SI-Z. BI-Z, Behavioral Indices Composite Score; SI-Z, Sleep disturbances Indices Composite Score; c, total effect; c′, average direct effects; c-c′, indirect effect. N = 817 (5 not included due to missing age).
Figure 2.
Figure 2.
Mediation model with composite scores as mediators and Hospital Anxiety and Depression Scale (HADS) as outcome. Values represent unstandardized regression coefficients. Values in parentheses represent estimations of 95% confidence intervals. Values with percentage represent the estimated percentage mediated effect. Covariates: sex, age, baseline values of HADS, BI-Z, and SI-Z. BI-Z, Behavioral Indices Composite Score; SI-Z, Sleep disturbances Indices Composite Score; c, total effect; c′, average direct effects; c-c′, indirect effect. N = 816 (5 not included due to missing age and 1 due to missing HADS score at baseline).
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References

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