Statistical analysis
death
SECONDARY, EVENT
Patients were analysed on an intention-to-treat basis unless they withdrew consent for the use of any data. Data are summarised by number of participants (percentage) for categorical variables and mean (SD) or median (IQR) for continuous variables.The published statistical plan, which planned to use a Mantel–Haenszel Chi-squared test to analyse the primary outcome, was modified (see Additional files The binary secondary outcomes were compared between groups with the same method. The time to clinical improvement (two points on the WHO scale) was compared between groups by using a competing risk analysis approach (Fine and Gray model) with escalation of respiratory support as a competing event; a two-point improvement in the clinical WHO scale was defined as a continuous uneventful improvement (i.e. without the need for escalating respiratory support [including increase in oxygen flow]), from the date of inclusion to a two-point decrease.The differences in durations (of oxygen therapy and hospitalisation) were compared by a Mann–Whitney A per-protocol analysis was performed in the study population restricted to patients of the intervention group who laid prone for at least 2 h each day during the daytime and patients of the usual care group who never laid prone. Days considered were those preceding the use of non-invasive ventilation, intubation, transfer to an ICU, death, weaning of oxygen therapy or discharge from the hospital, whichever occurred first.The above analyses were repeated in prespecified subgroups formed according to the stratification variables. Post hoc time-to-event exploratory analyses were conducted (see Additional file The analyses were conducted with R v. 4.0.2. (R Foundation for Statistical Computing). A two-tailed 