Statistical analyses
Outcomes were described for the phase preceding the COVID-19 pandemic (01/01/20-12/03/20) and several COVID-19 phases based on preventative measures in the Netherlands (see Fig. 1). These were: the first lockdown (13/03/20-31/05/20), release of most restrictions (01/06/20-13/10/20), the second ‘partial’ lockdown (14/10/20-14/12/20), the second ‘strict’ lockdown (15/12/20-19/01/21), and the lockdown with a curfew (20/01/21-12/03/21). Psychosocial outcomes during the COVID-19 phases were compared to pre-COVID-19 using linear mixed effects regression analyses, to account for repeated measurements, with domains of HRQoL, fatigue and caregiver distress as dependent variables and the COVID-19 phases as independent dummy variables. Clinical distress during the COVID-19 phases was compared to pre-COVID-19 using logistic generalized estimating equation modelling with an exchangeable covariance structure. Models were corrected for demographic and medical variables (age, sex, time since diagnosis, treatment status [on or off active treatment] and CNS tumor diagnosis). A p-value of 0.05 divided by the number of analyses conducted on (sub)scales of a questionnaire (e.g. for PedsQL generic: 0.05/6=0.008) was considered statistically significant.