Dangers of joint authorship of expert reports

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Dangers of joint authorship of expert reports


Can Multiple Experts Write an Expert Report?


Expert reports are subject to expert codes of conduct, court directions and civil procedure rules of the court and jurisdiction where the report is served. As stated in s79 of the Evidence Act 1995, the author of an expert report must have “specialised knowledge based on the person’s training, study or experience” and their opinion must be “wholly or substantially based on that knowledge”.

The same rules apply to any co-author who assists in drafting the report. In this context, co-author refers to anyone who makes a substantive contribution to the expert opinion in the report. It does not include the instructing solicitors or ExpertsDirect’s Quality Assurance Team, whose role is to guide the expert on the laws of evidence and the relevancy of their expert opinion. This guidance should never extend into co-authorship.

Although the practice of joint expert opinion is not uncommon in the United States,[1][2] it is much less common in Australia, where it is more likely for multiple experts to write separate reports. This approach reduces the risk of expert opinion being dismissed and increases the ease of cross-examination, as it is clear which author wrote which opinion. Each report is also self-contained; if one expert’s report should be considered inadmissible, it does not preclude the evidence of the other experts.

The Case Law

There has been extensive discussion in Australian caselaw whether joint expert opinions should be admitted into evidence.

In BrisConnections Finance Pty Limited (Receivers and Managers Appointed) v Arup Pty Limited,[3] Lee J recognised the prevalence of joint expert opinions in the United States.[4] Despite the statutory differences, Lee J deliberated that joint expert opinions are admissible if:

“… an opinion is the result of an application of the specialised knowledge of a proposed witness, but is reached following discussion and debate between the expert and another (even if the tentative or preliminary view of the expert is refined or changed by that discussion and debate, and involves, as a matter of fact, a consensus emerging, by reason of that process, between the initial view of the expert and the view of another)”. [5]

He contrasted this with “compromised opinions”, which he defined as:

“… opinions reached as a result of decision to ‘adopt’ an opinion, which opinion is not the result of an application of the specialised knowledge of a proposed witness, but as a result of a compromise between the proposed witness and another”. [6]

In this case, an expert had enlisted the help of his son in producing an expert report, but it was not clearly outlined who wrote which parts of the report. Lee J acknowledged that the father had more extensive experience and agreed with the assertion that the report was “infected with the cross-pollination of ‘specialised knowledge’” between the expert and his son. Lee J ruled that the report contained “compromised opinions” and was inadmissible:

“it is evident that opinions said to be held by [the expert’s son] were not based on his training, study or experience, but rather on the more extensive experience of [the father]. The pervading vice is that there is no way to identify who did what, on the basis of what, and whose specialised knowledge was deployed in forming the opinions.”[7]

In a more recent case, Scenic Tours Pty Ltd v Moore,[8] an expert was named a “problematic expert” for a number of reasons, one of which was for not disclosing the qualifications and contributions of another individual who assisted in writing his report:

“[The expert] did not reveal, until being cross-examined, that he had had considerable assistance from a manager of one of his travel agencies in preparing his report. There was no evidence as to that manager’s qualifications, training or experience in the travel industry. Nor did the fact of joint authorship of the report give the Court much confidence in assessing which opinions expressed in it were [his]”.[9]

In Ray Fitzpatrick Pty Ltd v Minister for Planning,[10] Jagot J declared a respondent’s initial expert report inadmissible on the grounds that it was not clear whether the nominated expert was the “ultimate author”; the respondent also failed to nominate the co-authors of the report as experts. Additionally, there was no evidence of whether the nominated expert “directly (or even indirectly) supervised” the interviews and modelling which formed the basis of the report.[11] Further, each author did not disclose the facts, and assumptions of fact, on which the opinions in the report are based and any examinations, tests or other investigations on which they have relied.[12]

Although the respondent had made all of the co-authors available for cross-examination, Jagot J found this problematic due to the inscrutability of the experts’ methodology and lack of clarity on who wrote which parts of the report. The opinion was considered untestable through cross-examination and productive of unfairness:

“The fact that the respondent is willing to make all the authors available for cross-examination does not answer (and indeed increases) the problems. The 2006 report does not disclose who was responsible for its various parts. In the circumstances set out above neither the applicant nor the Court should be burdened by an obligation to deal with four witnesses on this issue”. [13]

In Anderson v Holden Peel Projects Pty Ltd (Building and Property),[14] Senior Member S. Kirton preferred the expertise of a plumber over that of a construction company. The construction company produced multiple reports, with three different authors. The report did not disclose which person was responsible for which opinion,[15] nor did it specify the roles of each of the authors or the process undertaken to sign off on the report. Only one of the experts, the expert who signed off on the report, attended the Tribunal to give evidence. [16]

  1. Kirton further noted inconsistencies with the opinions of the experts. In one of the reports, an author stated that the core sample included a waterproof membrane. However, in oral evidence, the testifying expert asserted that there was no waterproof membrane. [17]

The construction company’s report did not comply with PNVCAT2 as it was difficult to determine whose specialised knowledge was applied in the expert report, nor was there a statement that the report was based on any of the experts’ specialised knowledge. When the testifying expert was asked in cross-examination whether the opinions in the report were his, another expert’s, or the Owners Corporation’s, he was only able to reply, “It’s not the Owners Corporation’s”.[17]


These judgments reveal that Australian courts are not opposed to joint expert opinions and find value in experts consulting with other experts to formulate a more well-informed opinion. However, the same rules still apply to any major contributors to a report—the report should specify their field of specialised knowledge, where in the report they have contributed, and how they have applied their specialised knowledge in providing that opinion.

Joint expert opinions also carry considerable risks, including:

  • Dilution of expertise, as seen in BrisConnections Finance Pty Limited (Receivers and Managers Appointed) v Arup Pty Limited. One expert may be seen as adopting the opinion of a more experienced expert, rather than forming their own opinion.
  • Inconsistencies in opinion, as seen Anderson v Holden Peel Projects Pty Ltd (Building and Property). This is especially problematic during cross-examination if the collaborating experts have not arrived at a consensus.
  • Difficulty in cross-examination if contributions are not disclosed. This is seen in Scenic Tours Pty Ltd v Moore and Ray Fitzpatrick Pty Ltd v Minister for Planning. Even if all authors were available for cross-examination, cross-examination will be untestable as it is not clear who authored which parts of the report.


It is important to be mindful of the rules of expert evidence and remember that they apply to contributing parties in the preparation of expert reports. In the case where a matter is complex, the option of having multiple experts writing different reports should be considered to minimise the risk of expert opinion being deemed inadmissible.


[1] Barker v. Valley Plaza, No. 12-4147, U.S. 10th Cir. 2013.

[2] Syngenta AG MIR 162 Corn Litigation, USDC (Kansas) Case No. 14-md-2591-JWL (2 Sept 2016).

[3] [2017] FCA 1268 (16 October 2017).

[4] Ibid at [45-46].

[5] Ibid at [48].

[6] Ibid.

[7] Ibid at [35].

[8] [2023] NSWCA 74.

[9] Ibid at [90].

[10] [2007] NSWLEC 791.

[11] Ibid at 31.

[12] Ibid at 33.

[13] Ibid at 32.

[14] [2020] VCAT 538.

[15] Ibid at [22].

[16] Ibid at [28].

[16] Ibid at [30].

[17] Ibid at [29].

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