Objective: Early improvement predicts good outcome in psychotherapy for eating disorders. Prior studies have examined change in body mass index (BMI) or Eating Disorder Examination Questionnaire scores (EDE-Q) as indicators of early response, but not both simultaneously. Little research has examined early change among Anorexia Nervosa (AN) samples treated with eating disorder-focussed cognitive behavioural therapy (CBT-ED). We studied the process of early change in a fine-grained way to better understand whether early response predicts later response and post-treatment outcomes in CBT-ED for AN, and how the changes in EDE-Q and BMI are related.
Method: Adults (N = 193) diagnosed with AN were treated with outpatient CBT-ED. We used bivariate Latent Change Score models to examine change in BMI and EDE-Q and relations between them.
Results: Early change in BMI was independent of early change in EDE-Q. Larger changes in EDE-Q over the first five weeks of therapy followed smaller ones over the next five weeks, meanwhile smaller changes followed larger ones. Early change was predictive of post-treatment scores.
Conclusion: Early change in BMI and EDE-Q during CBT-ED appear to be unrelated and follow different trajectories. Therefore, individuals declared as early responders may differ depending on which variable is used for the decision.
Keywords: CBT-ED; anorexia nervosa; bivariate latent change score; early response; eating disorders.