Methods Vignettes: Concurrent Evidence



Concurrent evidence is a method of hearing expert evidence used in court rooms, public hearings and inquiries. Its defining characteristic is that it replaces an adversarial process of evidence giving and questioning, pervasive in common law jurisdictions, with a process designed to be co-operative.

Experts are required to sit side by side, define issues together, question each other and take questions from the judge and parties. The idea is to create something more akin to a discussion that allows issues and understandings to emerge, become clearer and be viewed from multiple viewpoints simultaneously. It is sometimes referred to by other names such as ‘hot tubbing’, policy forum or expert panel but they have the same essential characteristic of experts giving evidence concurrently while being questioned and questioning each other.

The origins of the approach can be traced to the Australian legal system where it emerged informally in the civil courts in the 1970s and was formally adopted in the 2000s. It emerged in response to a general impression that experts were biased to the side that instructed them, making them obfuscatory and therefore expensive and inefficient. Going through each expert in turn was also seen to be confusing as the same issues would not be discussed by the relevant experts at the same time, making it difficult to compare opinions.

The approach has attracted widespread interest and has now spread to civil courts in other common law countries such as the UK, Hong Kong, Singapore, New Zealand and Canada. It has also been used in international commercial arbitration, regulatory board hearings and a range of quasi-legal settings such as public inquiries. Notable examples include the inquiry into the 1998 Sydney water crisis in Australia and the Goudge inquiry into the state of pathology and forensic services relating to child deaths in Canada.

What’s involved?

Justice Peter McClellan, the Australian judge widely acknowledged for popularising the method, has provided a clear summary of what the method involves (McClellan, 2010). He explains that there are variations but the process usually consists of the following stages:

  1. The experts prepare a written report of their opinions and exchange reports (standard practice for civil cases in many jurisdictions).
  2. The experts meet pre-trial, in the absence of lawyers, to discuss issues and prepare a bullet point document listing matters on which they agree and disagree (also standard practice in many jurisdictions).
  3. The novel part is that the experts are sworn in together at the trial to give evidence at the same time. The judge will often have used their pre-trial list to draw up an agenda. The experts have an opportunity to present their views and to question each other. The judge will direct the discussion and ask questions. Usually, the representatives will also have a chance to ask questions. At the end of the session the judge will usually ask the experts a general question to check that they feel they have had a chance to explain their positions fully.

The number and mix of experts giving evidence at a time can vary widely. It can be anywhere between two and twelve with widely varying mixes and types of expertise.

Broadening out and opening up?

The method has the potential to broaden out and open up expert appraisal by:

  • increasing the free flow of evidence giving, allowing consideration a wider diversity of information.
  • reducing partisanship, so allowing experts to acknowledge limits to knowledge and be more flexible in their views.
  • clarifying the reasoning behind knowledge claims, so helping to highlight areas of disagreement and/or uncertainty and therefore increasing transparency.
  • reducing confusion caused by delay between experts giving evidence on the same issue, giving time to better explore the range of opinions.

However, Gary Edmond (2009) makes a number of criticisms which suggest concurrent evidence may under particular circumstances have a closing down effect because:

  • the most commonly cited justification for concurrent evidence is efficiency and saving of court time. This could actually lead to experts giving a less complete picture of the evidence under time pressure.
  • it is nonetheless often focussed on a funnelling down to consensus and this can lead to a closing down of issues. This can happen behind closed doors in negotiations during the pre-trial meeting of experts. This is especially problematic if there is a natural hierarchy amongst the experts so that one expert asserts their views and other views are hidden.
  • the approach can be interpreted as replicating an idealised view of science (referred to by Edmond as Mertonian) that assumes that open discussion and peer review will allow for a consensus on the “truth” to emerge.
  • it doesn’t necessarily address the issue of how the experts are chosen. The method suggests that you can reduce bias at trial stage but the opposing biases may already be inbuilt from the selection stage.

In order for concurrent evidence to avoid these features and assist the broadening out and opening up of formal evidence hearings, it must be designed in ways that avoid these problems.

Roles, fit and limits

Concurrent evidence is a loosely defined method that does not have well developed guidelines to ensure that it is done in one particular way. This is following the principle that judges should be given wide latitude in deciding what evidence is needed, and how it is given, in any specific case.

This means that whether it broadens out and opens up very much depends on how it is applied, interpreted and led.

It would seem to have high potential where the overseers of the process are well informed on the issues, enthusiastic to explore them and have an understanding of inherent uncertainties in scientific evidence. It could have the opposite effect if they are focussed on saving time and money or funnelling consensus in a search for a perceived objective truth.

It will also depend on how the experts are chosen and grouped. If a broad range of experts, willing to engage with each other respectfully, are chosen and grouped together by issue rather than discipline then the interactions are more likely to lead to a questioning of how an issue can be viewed from multiple viewpoints. This should allow for the background assumptions of the different disciplines to be raised, leading to increased transparency and a broadening out and opening up of the debate.

References and further resources:

Instructional video produced by the Judicial Commission of New South Wales. “Concurrent Evidence: New methods with experts”:

Edmond, Gary. “Merton and the hot tub: Scientific conventions and expert evidence in Australian civil procedure.” Law and Contemporary Problems 72.1 (2009): 159-189.  (Download as PDF)

McClellan, Peter. “New Method with Experts-Concurrent Evidence.” Journal of Court Innovation 3 (2010): 259. (Download as PDF)


Material for this vignette was contributed by Charlie Dobson.