Expert Witness Independence: Reputation and Partisan Opinions

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Does a history of giving evidence for or against a plaintiff/defendant rule an expert witness as partisan?

The issue recently arose in the Monsanto Class Action, in which the Bayer-owned company is accused of selling their Roundup weedkiller product with knowledge of its carcinogenic effects. Parties to the action disagreed over the decision of Federal Court Justice Michael Lee to postpone any ruling of admissibility of evidence from experts engaged by class legal counsel. Whilst Monsanto argued that the previous reporting experience of the four experts (who had already given evidence against Monsanto in the US) hired by the complainants displayed an obvious bias against Monsanto, Counsel for the class welcomed Justice Lee’s conclusion that he had no statutory power under section 92 of the Evidence Act 1995 (Cth) to test substantial aspects of the expert evidence at the pre-trial stage.

Monsanto’s concerns here relate to the admissibility of expert evidence from seemingly compromised expert witnesses, and the court reaffirmed its position that issues of admissibility could not be addressed at the pre-trial stage. Section 135 of the Evidence Act would allow for the court to consider any prejudice in the evidence or status of expert witnesses.

However, Monsanto’s concern about its opponent’s expert witnesses may have also revolved around factors unfairly affecting the court’s perception of the persuasiveness of an expert report. To what extent can parties resist the potential for an expert’s historical influence or notoriety to unfairly shape how courts weigh expert evidence? If the evidence of those four experts held significant sway in US litigation, would Australian courts feel undue pressure to allow the evidence to do the same? And what could Monsanto do about this?


Judicial Bias

Beyond the power to select an expert, lawyers are mostly powerless to protect their cases from the historical fact of their expert’s reporting reputation and experience. Judgements in the public domain frequently mention expert witness names, and no one can eradicate the personal experience of judges with a particular expert and his or her testimony. Parties are, however, able to protect themselves from tendencies of the court to unfairly rely on its impressions of the expert witness’s reporting experience in its decision-making.

The rule against bias allows parties to make a complaint against judicial members whose impressions of expert witnesses may unfairly affect the outcome of the case. Whilst judges are indeed permitted to comment on the reliability of expert witness evidence, they are not permitted to actually or ostensibly apply broad, immaterial presumptions about expert witness credibility in deciding the outcome of a matter. If a judge does appear to do so, lawyers can rely on the rule against Actual Bias or Apprehended Bias.

  • Actual Bias

A claim of Actual Bias requires a party to prove that despite an expert’s persuasive evidence, the conclusion of the decision-maker was nonetheless swayed by prejudice which prevented the decision-maker from considering the expert evidence fairly and giving the evidence its due weight. Actual bias is exceedingly difficult to prove since lawyers must demonstrate how factors in the mind of the decision-maker have unjustly affected the outcome of the case.

  • Apprehended Bias

A party may make a claim against “apprehended bias” in the instance where “a fair-minded lay observer… ‘might entertain a reasonable apprehension that [the judge] might not bring an impartial and unprejudiced mind’” to the decision. (Webb v The Queen (1994) 181 CLR 41, 67 (Deane J)) This test requires that cases impart the appearance of justice to an informed member of the public who might observe the proceedings, reasoning, and outcome of the case.

To prove apprehended bias, the complaining party must explain how an informed layperson could plausibly perceive a comment, procedural decision, or circumstance of the decision-maker as evidence of an undue influence on the outcome of a case. Specifically, the party must articulate “a logical connection… between the identified thing and the feared deviation from deciding the case on its merits”.  (CNY17 v Minister for Immigration and Border Protection (2019) 375 ALR 47 [57] (Nettle and Gordon JJ))


Vakauta v Kelly [1989] HCA 44

In Vakauta v Kelly (1989) HCA 44 (‘Vakauta’), the High Court considered an appeal by the Government Insurance Office of New South Wales (‘GIO’) against a decision of a judge of the Supreme Court. GIO had admitted liability in an accident and the parties had attended a trial for the assessment of damages. At this trial, GIO had engaged three medical expert witnesses with a history of providing insurer-friendly expert witness reports, which the trial judge repeatedly criticised throughout the trial and in his Honour’s judgement.

The High Court drew particular attention to the following comments, amongst others, of the judicial member in the Supreme Court matter. All five judges of the High Court examined remarks the decision-maker from both the trial and the reserved judgement:


  • … I am not usually very impressed with the views of the other doctors, Drs Lawson, Revai and Dyball, who have been identified as the defendant’s doctors in this case, on the basis that those views are almost inevitably slanted in favour of the GIO by whom they have been retained, consciously or unconsciously.”
  • That unholy trinity…” (when referring to the three doctors)
  • Dr Lawson’s suggestion that the plaintiff could work in the casualty ward did not impress me. Neither did the remainder of his evidence, which was as negative as it always seems to be – and based as usual upon his non-acceptance of the genuineness of any plaintiff’s complaints of pain.”


The court found that the comments were sufficient to allow a reading of judicial bias. In particular, the targeted and derogatory commentary on Dr Lawson’s tendency to produce insurer-friendly reports could plausibly suggest that the Judge had decided the matter with more interest in “vindicat[ing] his preconceived and very strong adverse views about the reliability of Dr. Lawson as a witness” by awarding the matter to the claimant, rather than with an interest in deciding the matter on its merits. ([7] (Brennan, Deane, and Gaudron JJ)) Taken in the context of the Supreme Court judge’s censorious remarks about the defendant expert witnesses during trial, the final reserved judgement indicated that the judge “failed to consider the evidence in the case fairly and impartially, putting to one side his preconceived views about the GIO and its witnesses”. ([13]  (Dawson J)) The remarks could suggest to a layperson that his Honour had presumed the unreliability of the appellant’s expert witnesses and would therefore give their evidence marginal weight, regardless of the actual persuasiveness of its content. ([10] (Toohey J))



Parties have a choice as to whether they would like to take issue with what they perceive as ostensibly biased conduct but may not be as pragmatic as to wait to hear the outcome of the case. In cases where parties have waited too long to raise the issue, parties are said to have waived their right to the rule against bias.  (Smits v Roach [2006] HSCA 36; Vakauta v Kelly (1989) HCA 44)

In Vakauta, the Court confirmed that a party waives its right to the rule against bias when it awaits the outcome of a case before finding fault with the bias of a judge towards an expert. [5] However, in the circumstances of Vakauta, the reserved judgement reiterated and drew out the effect of earlier biased comments, thus re-enlivening the opportunity of Counsel to raise the issue of bias.


Is this enough? Our Recommendation

Lawyers may still question whether the rule against bias offers sufficient protection against unfair judgements of expert witness evidence. It is imaginable that in many cases, judges may not be so vocal about their preconceived impressions of experts and tacitly allow unfair prejudices to influence their decision-making.

We believe that the best form of guarding against such bias is to engage a strong expert witness. An expert who can explain their reasoning and conclusions cogently and persuasively is also one who can resist unfair representations of their evidence, as well as bolster their reputation within the court system.

In its class action case, Monsanto, if it does not raise the issue of expert witness prejudice under s 135 of the Evidence Act, may consider raising the rule against bias if the matter’s decision-makers perform or present any prejudiced action or status that can be perceived to unduly favour Monsanto’s opponents. But ultimately, the refutation of that claim depends on the ability of the claimants’ expert witnesses to present a persuasive case on the material facts of the matter to the court.

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