Statistical analyses
SECONDARY, SENSITIVITY
Data were managed using REDCap [Within the participants who were included in the modified intention-to-treat analysis (Analysis of primary and secondary outcomes were conducted on the modified intention-to-treat population and were based on a 2 (Drug; Oxytocin, Placebo) x 4 (Time; baseline wk 0, post-placebo lead in wk 3, post randomized treatment wk 15, follow-up assessment wk 27) x 2 (age group; 3–5 years, 6–12 years) mixed-design ANOVA. Age was entered as a pre-planned factor and our Data Safety Monitoring Board (DSMB) requested that we only recruit for the younger age group following interim analysis. Site was considered as an additional factor but was removed from models due to lack of significance. Greenhouse-Geisser corrections were applied when assumptions of sphericity were violated. For the CGI only, a 2 (Drug; Oxytocin, Placebo) x 3 (Time; post-placebo lead in wk 3, post randomized treatment wk 15, follow-up assessment wk 27) x 2 (age group; 3–5 years, 6–12 years) mixed-design ANCOVA was conducted on improvement scores, with baseline (wk 0) severity scores included as a covariate.To unpack interaction effects, planned simple contrasts were used, comparing each timepoint to study baseline (Visit 1). For contrasts that reached statistical significance, the sample was first split by age (3–5 years; 6–12 years) and repeated measures ANOVAs were used to compare scores between treatment conditions (oxytocin, placebo). Where appropriate, effect sizes (Cohen’s Sensitivity analyses of the primary outcome included group differences in SRS-2 Total Raw scores (i) separately in the subgroups of participants with a baseline SRS-2 Total Raw score at or above the sample median or with a baseline SRS-2 Total Raw score below the sample median, and (ii) in the per-protocol population (defined as all participants who completed the trial and had SRS-2 data available at each timepoint).Clinical changes were also evaluated for individual participants using the Reliable Change Index (RCI) [Analyses on treatment guess were conducted on participants with available treatment guess data at Visit 3. Chi-square tests were used to compare the proportion of treatment guesses between the oxytocin and placebo conditions. Safety analyses included all participants who were randomized to oxytocin or placebo (