A multiple-baseline evaluation of a brief acceptance and commitment therapy protocol focused on repetitive negative thinking for moderate emotional disorders

Repetitive negative thinking (RNT) in the form of worry and rumination has been identified as a particularly counterproductive experiential avoidance strategy implicated in the onset and maintenance of emotional disorders. The current study analyzes the effect of an individual, 2-session, RNT-focused, acceptance and commitment therapy (ACT) protocol in the treatment of moderate emotional disorders. Ten adults suffering from moderate to severe emotional symptoms according to the Depression Anxiety and Stress Scale-21 (DASS-21) and the General Health Questionnaire-12 (GHQ-12) participated in the study. Participants completed 5- to 7-week baselines without showing improvement trends in the DASS-21 or the GHQ-12. Afterwards, they received the ACT protocol, and a 3-month follow-up was conducted. A Bayesian approach to analyze clinically significant changes (CSC) for single-case experimental designs (SCED) was conducted, which required at least substantial evidence of the intervention effect and scores in the nonclinical range. Nine of the 10 participants showed CSC in the GHQ-12, and 7 participants in the DASS-21. The standardized mean difference effect sizes for SCED were computed, which facilitates comparison and integration of the results with group designs. Very large effect sizes were found for emotional symptoms (d = 2.44 and 2.68), pathological worry (d = 3.14), experiential avoidance (d = 1.32), cognitive fusion (d = 2.01), repetitive thinking (d = 2.51), and valued living (d = 1.54 and 1.41). No adverse events were found. RNT-focused ACT protocols deserve further empirical tests.