The analysis showed no effect for treatment condition (p = .27) or time (p = .26), but there was a marginally significant interaction of condition and time, F(1, 13) = 3.65, p = .078, partial η2 = .22 (a large effect). The interaction was dismantled using contrasts in a two-level MMRM. Results showed a similar pattern as other measures. Control participants showed a small and significant improvement from pre- to posttreatment, Mdiff = −5.82, SE = 1.86, t(120.71) = 3.12, p = .002, 95% CI [2.13, 9.52], effect size = .41, but no significant change from pretreatment to follow-up, Mdiff = −0.16, SE = 1.41, t(98.73) = −0.11, p = .91, 95% CI [−2.95, 2.63], effect size = .10. Participants in the ACT condition also showed a small and significant improvement from pre- to posttreatment, Mdiff = 4.88, SE = 1.79, t(117.38) = 2.73, p = .007, 95% CI [1.34, 8.43], effect size = .34, which was maintained through the follow-up period, Mdiff = 9.46, SE = 2.98, t(95.83) = 3.18, p = .002, 95% CI [3.56, 15.37] effect size = .47.
