Statistical analysis
Baseline characteristics were descriptively reported. T-tests and chi-square tests were used to examine potential differences in age, sex and tumor location between participants and non-participants (active or passive refusal), and between participants and patients who were not approached (due to severe illness/palliative care or logistical issues).
To examine differences in reported sleep between participants and healthy children, scores of the PROMIS questionnaires were compared to a mean score of 50, using one-sided t-tests. Statistical significance was considered as a P -value of <.05. The percentage of moderate and severe sleep problems was described by using the questionnaire-specific cut-offs25 and compared to the normal population by using non-parametric chi-square tests.
Linear regression models were used for comparing actigraphic sleep estimates between the participants and healthy children. As sleep estimates are age-dependent, regression models were adjusted for age28.
Risk factors for impaired sleep were explored by building linear regression models. Demographic and medical variables relevant for sleep outcomes were examined with univariate analyses. Variables with aP -value of <.10 were subsequently added to a multivariable model. A P -value of <.05 was considered significant. All analyses were carried out with IBM SPSS Statistics version 26.0.0.1.