When Is Improvement Possible? A Necessity‐Based Analysis of Short‐Term Eating Disorder Symptom Improvement During Inpatient Treatment

OBJECTIVE: Eating-disorder-specific functional impairment may represent a boundary condition for treatment response, yet this possibility has rarely been examined. We investigated whether baseline functional impairment constrains short-term eating-disorder symptom improvement, indexed by change in EDE-Q Global scores during inpatient treatment using a necessity-based framework. METHOD: We retrospectively analyzed 462 inpatients who completed the Eating Disorder Examination Questionnaire (EDE-Q 6.0) at admission and discharge. Functional impairment (Clinical Impairment Assessment, CIA), general psychopathology (SCL-90-R GSI), and body uneasiness (BUT-GSI) were assessed at baseline. Short-term eating-disorder symptom improvement was defined as clinically meaningful improvement based on the Reliable Change Index and as continuous change in EDE-Q Global scores. Necessary condition analysis with permutation testing and bottleneck analysis was applied, with subgroup analyses for anorexia nervosa versus non-anorexia nervosa. RESULTS: ED-specific functional impairment emerged as a statistically significant necessary condition for clinically meaningful improvement (NCA d = 0.167, p = 0.011) and symptom change (d = 0.159, p = 0.002). Neither general psychopathology nor body uneasiness met criteria for necessity. Bottleneck analysis showed that larger symptom reductions occurred only above increasing CIA thresholds. Necessity effects were robust in AN but absent in non- diagnoses. DISCUSSION: Functional impairment appears to constrain short-term inpatient EDE-Q improvement in anorexia nervosa, whereas no necessity effect was observed in non-anorexia nervosa diagnoses. These findings suggest that ED-specific functional impairment may function as a boundary condition for short-term EDE-Q improvement in anorexia nervosa within the present sample, whereas no corresponding necessity effect was observed for general psychopathology, body uneasiness, or non-anorexia nervosa diagnoses.