Statistical analyses
For all variables the assumption of normality was checked and corrected for, if necessary. IBM SPSS 27 was used for the statistical analyses (IBM Corp., Armonk, USA). Demographic and baseline data of the two groups were analyzed using two-tailed independent To determine the efficacy of the short add-on therapy, per protocol analyses were performed (see The Dutch Trial Register; registration number NL9368; Individual-level change scores were calculated using Reliable Change Indices (RCI; (In order to assess whether the effects of the add-on sleep intervention were maintained from post-treatment to 3-month follow-up, paired sample 