highly significantP <.001
Finally, a linear mixed-effects regression analysis on SPIN scores over the intervention period (including baseline) modulated by group (intervention vs waitlist control) and controlling for age, sex (RCT 2 only), and the plateau effect of SPIN scores over time (week 2 ) revealed a highly significant main effect of week (RCT 1: mean β −3.149, SD .398, t 392.719 =−7.922, and P <.001; RCT 2: mean β −3.388, SD .249, t 1855.835 =−13.589, and P <.001) and a group × week interaction in both RCTs (RCT 1: mean β 1.691, SD .566, t 391.935 =2.99, and P =.003; RCT 2: mean β 1.588, SD .340, t 1846.697 =4.669, and P <.001), suggesting that SPIN scores declined in both groups, but this decline was significantly steeper in the intervention group (see Table S1 in Multimedia Appendix 1 for details).