When might issues of independence and credibility go to the admissibility of an expert’s evidence

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McNickle v Huntsman Chemical Company Australia Pty Ltd (Evidentiary Ruling)


McNickle v Huntsman Chemical Company Australia Pty Ltd (Evidentiary Ruling) [2023] FCA 1268

This evidential ruling in a class action concerning the alleged carcinogenic effects of Roundup weedkiller was the result of an application made by the respondents (collectively known as Monsanto) to exclude the expert evidence of Dr S, an expert called by the representative applicant in the proceedings (the applicant).

Details of the background to the class can be found in McNickle v Huntsman Chemical Company Australia Pty Ltd (Expert Evidence) [2021] FCA 370 (the 2021 Decision).


Both Dr S, and the Monsanto’s expert, Dr D, were to participate in a conclave, “Conclave F”, to take place in early October 2023. Three days prior to the start of Conclave F, solicitors for Monsanto notified the applicant’s solicitors that they did not intend to call Dr D and therefore a concurrent evidence session was unnecessary.

Monsanto’s solicitors subsequently advised that they intended to rely on the evidence of Dr S, including that evidence in the joint report resulting from Conclave F, in which the opinions of Dr D were redacted.

Following the cross-examination of Dr S, Monsanto made an application to the court to exclude his evidence pursuant to s 135 of the Evidence Act 1995 (Cth) (the Act) on the basis that “it might give rise to a danger of unfair prejudice or be misleading or confusing”. [13]

Expert Evidence

In what Lee J characterised as a “direct and concerted attack” on Dr S’s independence in providing opinion evidence, his Honour focussed on the following five key aspects of the cross-examination of Dr S:

  • In the over 100 reports given by Dr S in 49 separate proceedings concerning the alleged carcinogenic effects of Roundup, he consistently expressed the view that the product was carcinogenic to humans.
  • Dr S maintained a fixed view that Monsanto has engaged in unethical and criminal conduct in seeking to interfere in the publication of scientific research on the carcinogenic effects of glyphosate, an active ingredient in Roundup, and had referred to emails said to corroborate his allegations (although those emails were not produced or provided to the court).
  • Parts of the primary report authored by Dr S dated September 2021 were a “cut and paste job” of reports he had previously authored in Roundup litigation in the United States, and this demonstrated that he was not bringing an independent mind to his evidence in these proceedings.
  • Dr S had said that his approach to giving expert evidence in these proceedings was broadly similar to his approach to giving expert evidence in the United States and as such he had misapprehended the role of an expert in the Anglo-Australian legal system.
  • In proceedings commenced in the United States, Dr S had referred other experts to testify for plaintiffs knowing that they would give evidence consistent with his opinions and therefore was not “truly independent about the issues and about their view”.


While Lee J had flagged in the 2021 Decision that it would be advantageous to deal with any attack on the independence of any of the experts sooner rather than later and the possibility that an order facilitating an advance ruling pursuant to s 192A of the Act may be appropriate (which permits the court to make a finding or give a ruling on questions about the admissibility of evidence before that evidence is adduced in the proceedings), the applicant opposed this course of action.

The applicant had submitted, both in the course of the hearing resulting in the 2021 Decision and for the purposes of the present application, that issues concerning a lack of independence or impartiality on the part of the expert can only go to weight, and not admissibility. In support of its submission, the applicant cited Rush v Nationwide News (No 5) [2018] FCA 1622 at [36] in which Wigney J stated that objectivity and independence were not preconditions of a competent expert witness.

The court held, as it did in the 2021 Decision, that there may be circumstances where a lack of impartiality or objectivity could go to admissibility and not just weight. For example, in circumstances where the court is required to consider whether to exclude expert evidence under s 135 of the Act, a lack of independence, objectivity or impartiality of the expert may result in the court concluding the evidence would be of such limited assistance that it would be unfairly prejudicial or result in an undue waste of time.

The court agreed with the applicant’s submission that the scientific material adduced from any expert in the proceedings should be admitted irrespective of whether that expert held any fixed view or felt any animosity towards a party, and admitted the opinion evidence of Dr S. The probative value of Dr S’s evidence was not outweighed by the danger of unfair prejudice or relevant confusion, and the matters raised by Monsanto could be “dealt with through the prism of an assessment of the weight of the evidence”. [27]

Key takeaways

  • Where an expert has consistently provided opinions of the same nature in previous proceedings addressing similar issues, that will likely open the expert to an attack on their independence and objectivity.
  • While issues of expert independence and impartiality go to the weight to be given to that evidence, there may also be circumstances in which those issues go to the admissibility of that evidence.
  • In situations where the court must decide whether to exclude expert evidence according to s 135 of the Act, the court may deem the evidence unhelpful to the extent that it could lead to unfair prejudice or a waste of of time if the evidence reveals that the expert lacks independence, objectivity, or impartiality.


Read the full decision here.

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