Evaluating the predictive validity of purging disorder by comparison to bulimia nervosa at long‐term follow‐up

OBJECTIVE: The current study sought to examine the predictive validity of the purging disorder diagnosis at long‐term follow‐up by comparing naturalistic outcomes with bulimia nervosa. METHOD: Women with purging disorder (N = 84) or bulimia nervosa (N = 133) who had completed comprehensive baseline assessments as part of one of three studies between 2000 and 2012 were sought for follow‐up assessment. Nearly all (94.5%) responded to recruitment materials and 150 (69% of sought sample; 83.3% non‐Hispanic white; 33.40 [7.63] years old) participated at an average of 10.59 (3.71) years follow‐up. Participants completed the Eating Disorder Examination, the Structured Clinical Interview for DSM‐IV, and a questionnaire battery. Diagnostic groups were compared on eating disorder (illness status, recovery status, and eating pathology) and related outcomes. Group differences in predictors of outcome were explored. RESULTS: There were no significant differences in eating disorder presence (p = .70), recovery status (p = .87), and level of eating pathology (p = .17) between diagnostic groups at follow‐up. Post hoc equivalence tests indicated group differences were smaller than a medium effect size (p's ≤ .005). Groups differed in diagnosis at follow‐up (p = .002); diagnostic stability was more likely than cross‐over to bulimia nervosa for women with baseline purging disorder (p = .004). DISCUSSION: Although purging disorder and bulimia nervosa do not differ in long‐term outcomes, the relative stability in clinical presentation suggests baseline group differences in clinical presentation may be useful in augmenting treatments for purging disorder. PUBLIC SIGNIFICANCE STATEMENT: While purging disorder is classified as an “other specified” eating disorder, individuals who experience this disorder have comparable negative long‐term outcomes as those with bulimia nervosa. This highlights the importance of screening for and treating purging disorder as a full‐threshold eating disorder.