The essay maintains that the WTO Appellate Body's concepts and terminology concerning a claimant's burden of proof-the concepts of prima facie case, presumption, and burden shifting-are disturbingly ambiguous and potentially misleading. This is so whether one thinks of these terms from either a common law or a civil law perspective. In the face of the current ambiguity, a future panel might understand the AB's prima facie case concept to require an overwhelming level of proof from the claimant. On the other hand, a different panel might allow a rather weak level of claimant's proof to meet the prima facie requirement, and then shift the full burden of proof to the respondent. Neither of these results would be justified. An important task of future AB decisions should be to clarify the existing ambiguity and to develop a more conceptually sound use of burden of proof terminology. The essay argues that the AB should abandon its current terminology (prima facie case, presumption, and burden shifting) and should simply state that the complaining Member bears the burden of proof on its basic claim and that this burden-meaning essentially the burden of persuasion-does not shift during the course of the proceeding. The reverse would hold for the responding Member's defenses.
And from the conclusion:
To summarize, one can read the AB decisions on burden of proof—albeit by employing a considerable amount of interpretive generosity—as saying that the burden of persuasion, which is the key concept, rests on the claimant as to the claimant’s basic claim of a WTO violation and does not shift during the course of the proceeding. But such a reading is not self-evident. Without more clarity, the current ambiguity that attends the AB’s burden-of-proof formulations can lead to serious misunderstandings and errors, especially at the panel level. Those errors might disadvantage either side in a litigated dispute. A panel might understand the AB’s prima facie case concept to require a much too overwhelming level of proof from the claimant; since, after all, such a case seems to have serious consequences for what is required of the respondent in rebuttal. On the other hand, a different panel might allow a rather weak claimant’s case to meet the prima facie requirement and then effectively reason that the full burden of proof is shifted to the respondent. These effects might even occur inside the panel’s conference room without being expressed in its published decision or otherwise coming to light.
The upshot then is that the AB should clarify the ambiguity created by its U.S.–Shirts and Blouses and EC–Hormones formulations. It should clarify what exactly it means by burden of proof, prima facie case, and presumption. If the generous interpretation offered above is correct, the AB’s future decisions could spell that out and eliminate or clarify the confusing discussion of a presumption that shifts an “onus” to the respondent. The AB could abandon altogether the concepts of prima facie and presumption—which seems to be the preferable choice—or the AB could interpret these concepts in the “generous” way suggested above so as to render them essentially inoperative. On the other hand, if the generous interpretation suggested above is not correct, then one would hope that the AB would not wait long before explaining more clearly its understanding of the concept of burden of proof in the WTO system and the reasoning that supports that understanding.
At first glance, this sounds right to me. I've always found the emphasis on burden of production/prima facie case, etc., rather than burden of persuasion, to confuse the issue a bit.