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Evidence in International Arbitration: Evaluation Criteria

(extract from Konstantin Pilkov. Evidence in International Arbitration: Criteria for Admission and Evaluation. Arbitration. – 2014. – Vol. 80. – Issue 2 2014)

It is commonly recognised that the admissibility of evidence does not automatically guarantee that the evidence will be considered as having probative value. There are more or less explicit relevance, admissibility and materiality criteria for determining whether a piece of evidence is admissible, whereas the methods for weighing evidence and determining the sufficient level of proof are subjective and somewhat inexplicable.[1] The weight of the evidence usually refers to its persuasive effect on the arbitrator’s mind. It is within the discretion of the tribunal to evaluate the evidence submitted by the parties, though the parties can agree on the sufficiency, as will be discussed later.

The weight of the evidence includes questions of credibility (reliability) and the evaluation of inferences which can be made from the evidence.


The ultimate question for any evidence is whether it constitutes reliable proof of what it is offered to prove. This, of course, turns on a closer inspection of the credibility or reliability (both words are used as synonyms of the other) of the evidence in question. The assessment of credibility is one of the functions of an arbitrator when weighing up evidence. At the admissibility stage the evidence is required to be prima facie credible, that is, it must ave sufficient indicia of reliability and authenticity to establish that it appears to show what it is offered to prove. The above definition is of course circular, in that it refers to the “reliability and authenticity of the evidence” in defining “credibility of the evidence”. To put things more simply we can define “credibility” as the capacity of being worthy of belief or confidence, trustworthy.

When the reliability of a document is under investigation the question of its authenticity is logically prior to the question of reliability. An authentic document—i.e. not a forgery—may or may not be reliable evidence of what it purports to show; and yet, if a document is not authentic it is hard to imagine how it could be helpful. As a result, the authenticity of a document is often considered to be a precondition for its use in an arbitration proceeding.

Depending on the nature of the evidence and the manner in which it is introduced, a number of different indicators (internal or external) might be applied to assess its reliability.

Internal indicators of reliability of a document include elements of the document itself, such as signatures, the form of handwriting, etc. External indicators might rely on other evidence: testimony about how a document was obtained, expert testimony on its authenticity, etc.

There are also many techniques used when deciding on the reliability of material or testimonies that contradict each other (e.g. where the inconsistency is between a current and a prior assertion of fact, the more recent assertion generally is disregarded in favour of the earlier assertion).

The tribunal can admit relevant and admissible evidence even though the credibility is in doubt. This admission does not mean that the tribunal cannot afford that evidence decreased probative value. Ultimately, it is very unlikely that the tribunal would decide to not admit something into evidence because its authenticity has not been established. In fact, it might be better to admit that document as the reliability of evidence can be fully assessed in its entirety with all other evidence. Besides, if a document is revealed to be a forgery, it is the document itself that proves the lack of authenticity, therefore its admission is necessary.


To carry its burden of proof, a party has to offer sufficient evidence. It is probable that it is because this statement is self-evident that the term “sufficiency” is almost never mentioned in arbitration rules. In assessing the sufficiency of evidence the arbitrator must determine whether there is any valid line of reasoning and permissible inferences which could lead a rational person to the conclusion reached by the arbitrator on the basis of the evidence.

Basically, sufficiency is not a criterion of a single piece of evidence, but rather the point at which the standard of proof is met. After reaching that point any additional evidence, though it is relevant and admissible, does not add anything material to the process of proving the fact.

Although the sufficiency can be finally assessed only in the process of weighing the evidence, the tribunal can take the initiative to manage the case by indicating in advance the evidence that it considers necessary to establish the prima facie proof of certain facts at issue. In doing so arbitrators should adhere to the due process and impartiality principles of arbitration proceedings.

Party Autonomy and Arbitrators’ Discretion

In the legal literature analysing the roles of the parties and the tribunal in evidentiary matters, it is often concluded that the rules governing arbitral proceedings make it clear that the admissibility, relevance, materiality and weight of any evidence are for the arbitrator to determine. Sometimes it is considered that the tribunal itself determines the relevance, materiality and probative value of all evidence submitted by the parties, and does not need to hear arguments from the parties concerning these matters. It is thus for the parties to submit the evidence and for the tribunal to evaluate it.

We would rather tend to the approach that allows the parties to retain autonomy and control over the evidentiary issues, even though the parties rarely use their autonomy in that way. The majority of arbitration laws do establish an environment in which the parties can agree on the application of almost any criteria for the evidence. As noted by Holtzmann and Neuhaus the UNCITRAL Model Law art.19(2) specifies that the power conferred on the arbitral tribunal includes the power to determine the admissibility, relevance, materiality and weight of any evidence. Of course, this provision is not mandatory and is therefore subject to the parties’ will. Alternatively, they can agree on particular rules of evidence, fori example that certain evidence should be deemed inadmissible, or that a certain kind of document be sole type of evidence. In this case, the arbitral tribunal should abide by that choice.[2]

Of all the criteria used, the inadmissibility of particular evidence (e.g. special contractual rules which exclude certain materials from evidence) and the issue of sufficiency are the two criteria on which the parties most frequently agree. Though it is the arbitrators’ function to determine whether the evidence in its entirety would rationally support a party’s allegation, the parties may agree on what may constitute sufficient evidence (e.g. by way of indicating in the contract a document that constitutes sufficient evidence of fulfilment of a contractual obligation).

The inadmissibility of illegally obtained evidence is a significant element in compliance with public policy rules. That is why in deciding on the admissibility of evidence the tribunal cannot be as flexible as in any other evidentiary matters. In deciding on the admissibility of evidence the autonomy of the parties and the tribunal may not be contrary to international public policy.

In any case, even if the parties rely on the tribunal in matters related to the application of the criteria for evidence, this only means that the parties do not introduce any specific rules regarding how the relevance, materiality and other criteria should be “measured”.

However, when a party submits evidence the opposing party should be provided with an opportunity to comment on the relevance, materiality, admissibility or probative value of that evidence.


As we have seen the threshold for admitting evidence in international arbitral tribunals is typically quite low, so admissibility, the key question in much of the legal discussion in courts in common law countries, is not a crucial issue in arbitration. Arbitrators focus more on the evidentiary weight they are going to give the evidence.

The basic prerequisites of the admissibility of any kind of evidence in international arbitration are its relevance and materiality. In general, if evidence is shown to be relevant, material, prima facie credible, and is not barred by an exclusionary rule, it is admissible.

The liberal application of these seemingly simple evidentiary rules is necessary to avoid sterile legal debate over admissibility so that the tribunal can concentrate on the pragmatic issues of the case. The tribunal should not, however, be loaded with excessive unnecessary materials. From that perspective it might be reasonable for the tribunal to determine that when introducing documents the submitting party must provide a short description of each document, clearly specifying its relevance, materiality and probative value.

Though in international arbitration the trier-of-fact is not a civilian jury, but a professional fully capable of admitting evidence and rendering objective determinations about the probative value at the end of the proceeding, questions of admissibility should be decided initially, especially if there are claims that any privilege rules apply or if any violation of international public policy is shown. Consideration of any such matters should not lead the procedure into technical formalities.

Three rather different approaches might be applied when deciding on admission of evidence, ordering production and exclusion: the relevance and materiality of the evidence submitted by a party must be shown for it to be admitted; the relevance and significant materiality must be stated by a party and recognised by the tribunal for the production of evidence to be ordered; for evidence already admitted to be excluded it must be manifestly irrelevant.

The above “standards” do not apply when dealing with admissibility sensu stricto, because any inadmissible evidence needs to be refused in admission, excluded or refused in ordering for production.

The criteria for the admission and evaluation of evidence discussed in this article ave very much connected to each other. They may be separated and grouped for convenience only. In practice the necessity for the application of any of the criteria for evaluation may arise at the admissibility stage. The assessment of the materiality of any additional evidence requires the admitted evidence to be evaluated. The categories of relevance, materiality and weight of evidence are dynamic—anything that was irrelevant to the case may become relevant while the case is in progress. The admissibility and reliability of evidence are more static criteria; they are almost exclusively attached to the evidence itself and have little relation to the case and other evidence. If the authenticity and thus the reliability of a document is in doubt it is so irrespective of the essence of the case, even if the authenticity was put in doubt because of contradictions between that document and the set of other materials.

Finally, we must emphasise that party autonomy extends also to evidentiary issues and the application of criteria for evidence, and being a crucial value cannot be negatively affected. The arbitral tribunal should abide by the agreement of the parties unless it is contrary to international public policy.

by Konstantin Pilkov

Arbitration Law Firm Ukraine Evidence in International Arbitration: Criteria for Admission

Konstantin Pilkov. Evidence in International Arbitration: Criteria for Admission and Evaluation. Arbitration. – 2014. – Vol. 80. – Issue 2 2014 Full article is available here and may be downloaded in PDF

[1] Audun J?sang and Viggo A. Bondi, “Legal reasoning with subjective logic” (2001) 8(4) Artificial Intelligence and Law 290.

[2] H.N. Holtzmann and J.E. Neuhaus, A Guide to the UNCITRAL Model Law on International Commercial Arbitration: Legislative History and Commentary (The Hague: Kluwer Law, 1995), p.566.

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