Are Anorexia Nervosa and Bulimia Nervosa Separate Disorders? Challenging The 'Transdiagnostic' Theory of Eating Disorders

Background: Anorexia nervosa (AN) and bulimia nervosa (BN) are classified as separate and distinct clinical disorders. Recently, there has been support for a transdiagnostic theory of eating disorders, which would reclassify them as one disorder. Objective: To determine whether AN and BN are a single disorder with one cause or separate disorders with different causes. Method: Hill's Criteria of Causation were used to test the hypothesis that AN and BN are one disorder with a single cause. Hill's Criteria of Causation demand that the minimal conditions are needed to establish a causal relationship between two items which include all of the following: strength of association, consistency, temporality, biological gradient, plausibility, coherence, experimental evidence and analogy. Results: The hypothesis that AN and BN have a single cause did not meet all of Hill's Criteria of Causation. Strength of association, plausibility, analogy and some experimental evidence were met, but not consistency, specificity, temporality, biological gradient, coherence and most experimental evidence. Conclusions: The hypothesis that AN and BN are a single disorder with a common cause is not supported by Hill's Criteria of Causation. This argues against the notion of a transdiagnostic theory of eating disorders. Copyright (c) 2008 John Wiley & Sons, Ltd and Eating Disorders Association.