70 Chapter 3 superiority of either a more intensive DBT-program or a dose-matched CBT-program, the DBT-BED program in this study may possibly have been as efficacious as CBT if CBT was dose-matched. Also, again contrary to our expectations, we did not detect any differences in favor of DBT-BED on measures related to emotion regulation. Indeed, at end of treatment, CBT+ outperformed DBT-BED on emotional dysregulation. This seems remarkable given the theoretical foundation of both therapies with DBT-BED targeting emotion regulation and CBT targeting dietary restraint and other behavior originating from the overvaluation of weight and shape. Possible reasons for failing to find differences may be related to limited statistical power or to increased treatment time in CBT+. Concurrently, to stay close to clinical practice we did not control for content and therefore conceptual overlap may have occurred. Differential effects of both therapies were possibly compromised because of this. However, it should be noted that most findings on the emotion regulation measures in this study are in line with Safer and colleagues (2010) who found a consistent lack of differential impact with a broad range of emotion-regulation measures comparing DBT-BED to an active controlled for content comparison. Also, in individuals with bulimia nervosa, CBT has been found to produce decreases in emotion dysregulation (Peterson et al., 2017). This suggests that decreases in emotion dysregulation might not be attributable to the specific emotion regulation techniques used in DBT-BED, but to therapeutic elements shared across various treatments. Apart from self-esteem, no significant differences in reduction between the groups were found on measures related to general psychopathology. Depressive features improved considerably in both groups. Improvements in OBE episodes seemed to diminish slightly between end of treatment and follow-up in both groups but stayed, on average, below the diagnostic threshold (< 4 OBE episodes in 28 days). This is in line with previous findings (e.g. Chen et al., 2017). In addition, a substantial percentage of patients in both groups reached clinically meaningful change in eating disorder psychopathology. Percentages were higher for CBT+ at both end-of-treatment and follow-up, but these differences were not significant. The study has several limitations. One major limitation of this study is the difference in dosage between DBT and CBT+, which compromises our ability to draw solid conclusions about the observed differences in outcome. A second major limitation is the limited sample size. With higher power we may have found more, and more robust, differences
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