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Witness evidence in international arbitration is generally prepared by witness statements these days. A witness statement is a written account of the testimony that a witness wishes to deposit in an arbitration. In the majority international arbitration cases, an oral examination then follows the typical common law pattern of direct examination – cross-examination – re-examination. If the oral testimony is prepared by written witness statements, it has also become almost standard practice that the written statement stands as direct evidence. If so, there is no direct examination, or only a very short one, and the witness’ examination directly starts with cross-examination.

The dichotomy of a written witness statement and other testimony leads to problems if the witness from whom a written witness statement was submitted to the record does not appear at the hearing for his or her examination. If so, the question arises whether the witness statement can still be accepted as witness testimony, or whether it has to be disregarded. Unless the parties reach an agreement in this regard, the matter has to be decided by the arbitral tribunal. Guidance on the issue can be obtained from the IBA Rules on the Taking of Evidence in International Arbitration (2010) (“IBA Rules”). According to Art. 4 (7) IBA Rules, the arbitral tribunal shall disregard a witness statement if a witness was required to appear at the hearing but fails to appear without a valid reason. Such valid reasons could exist is form of illness, travel restrictions or other severe reasons. More generic reasons such as “urgent other business” or other will generally not be accepted by arbitrators as a valid excuse.

If the arbitrators arrive at the conclusion that no such valid reason exists, so that the witness statement of the no-show witness shall be disregarded, an interesting psychological question arises: Is it at all possible to disregard the written statement? Can an arbitrator unring the bell once he or she has seen and read the witness statement? Psychological research suggests that this is not the case. Sussman (Sussman, American Review of International Arbitration, 2013/Vol. 24, p. 491 et seq.) reports experiments with American judges concerning the impact of inadmissible evidence on their decision making process. Each of the experiments included two peer groups who were confronted with an argument that certain documents or information presented by the other side were privileged or otherwise inadmissible so that they should be disregarded. The argument was sound so that 75 – 80 % of the test judges in fact declared the documents or information to be inadmissible. The difference between the two peer groups was that one peer group was provided with the information that was later declared inadmissible, while the other was not. All experiments confirmed that the judges who were given the information that was later declared inadmissible were influenced by the information in their decision making. For example, one experiment included a document claimed to be protected by attorney-client privilege that was highly damaging to the claimant’s case. 55 % of the judges in the peer group who did not see the document found in favor of the claimant; but only 29 % of the judges in the peer group who did see the inadmissible document found in favor of claimant. Accordingly, even though the judges knew that the document was inadmissible and even ruled out the information them, they still considered it and took it into account.

It is suggested that the same effect is likely to materialize in regard of witness statements that arbitrators have to disregard because a witness does not appear for giving oral evidence without a valid reason.

Are there remedies?

So are there remedies? It is suggested that the described effect is difficult to overcome because to a great extent, it works subconsciously. Simply not reading witness statements unless arbitrators know for sure whether witnesses will show up for the hearing is not an option because arbitrators need to prepare. But arbitrators who are aware of this effect are in a better position to self-monitor the decision making process when finding themselves in the described situation. They should carefully listen to their inner voice for signals indicating that the incriminating witness statement is on their mind when deciding the case. Another option to address the issue is to avoid the situation in the first place. If, for example, an arbitral tribunal believes that the non-appearance of a witness was foreseeable for the party, or maybe was even planned, the tribunal could punish the respective party in terms of costs. Parties who are aware of such sanctions will take more care in assuring that only witness statements for witnesses who are able and willing to appear at the hearing are submitted to the record.


Ragnar Harbst is a partner in the Frankfurt office. He has acted in numerous international arbitration proceedings with a focus on disputes related to construction and infrastructure.