Moderators of treatment effect in a randomised controlled trial of single- and multi-family therapy for anorexia nervosa in adolescents and emerging adults.

Introduction: Multi-family therapy for anorexia nervosa (MFT-AN) is a novel, group-based intervention that intensifies single-family therapy for anorexia nervosa (FT-AN), with the aim of improving outcomes. The current study explored treatment moderators in a randomised controlled trial (N = 167) of FT-AN and MFT-AN for young people (adolescents/emerging adults aged 13-20 years) with anorexia nervosa.

Methods: Data were analysed using multiple linear regression. Six hypothesised baseline participant and parent factors were tested as possible moderators of treatment effect on end-of-treatment and follow-up percentage of median Body Mass Index (%mBMI); age, eating disorder symptom severity, perceived family conflict (young person and parent ratings) and parent-rated experiences of caregiving (positive and negative).

Results: Greater parent-rated positive caregiving experiences moderated treatment outcomes at follow-up (β = -0.47, 95%CI: -0.91, -0.03, p = 0.04), but not end-of-treatment. Participants who had fewer parent-rated positive caregiving experiences at baseline had higher weight at follow-up if they had MFT-AN compared to FT-AN. No other hypothesised baseline factors moderated treatment outcome (p's > 0.05).

Discussion: The current study suggests MFT-AN may be indicated for families who present with fewer positive caregiving experiences to treatment. The MFT-AN group context may help to promote mentalisation and hope for these families, which may be harder to achieve in single-family treatment. Future research is needed to empirically evaluate how and why MFT-AN supports this group more.

Trial registration: ISRCTN registry: ISRCTN11275465, registered 29 January 2007.