Quantum evidence: what the Federal Court expects (and what will fail)
Recent authority from the Federal Court reinforces a point that is often underestimated in construction disputes: quantum evidence must be independently verifiable, transparent in method, and properly proved. Where it is not, even otherwise plausible claims may fail.
In Lucas Earthmovers Pty Ltd v Anglogold Ashanti Australia Ltd [2019] FCA 1049, White J delivered a clear warning on the limits of expert quantity evidence that rests on assumption rather than analysis.
Independent measurement is not optional
The Court accepted that a quantity surveyor could have independently assessed the relevant quantities, but emphasised that this did not occur. The expert did not undertake their own measurement of the as-built quantities and instead proceeded on the basis that the contractor’s pleaded quantities were correct ([590]–[591]).
This was fatal. The Court made clear that quantum experts are expected to test, not adopt, the figures on which their opinions rely.
Assumptions are not evidence
A central deficiency identified by the Court was that the expert evidence rested on assumed correctness of underlying data, rather than demonstrated proof. The quantities had been derived from a summary spreadsheet prepared by another individual, but:
the underlying workings were not produced,
there was no evidence explaining how the quantities were calculated, and
no witness could confirm the data sources or methodology used ([589]–[591]).
White J noted that this left the Court unable to assess whether the quantities claimed were reliable.
Proper substantiation is expected industry practice
Under cross-examination, it was accepted that, in ordinary practice, an assessor or superintendent would require substantially more material before certifying quantities, including:
original datum lines,
original drawings,
final as-built drawings, and
full workings showing how volumes were derived [590].
The absence of this material meant that the expert opinion lacked the factual foundation necessary to make it persuasive.
The consequence: deficiencies in proof, not merely weight
The Court did not treat these issues as minor matters going only to weight. Instead, it concluded unequivocally that there were deficiencies in the proof of quantities [593].
This distinction matters. Where proof is deficient, the claim itself may fail regardless of how reasonable the claimed costs might appear in the abstract.
Key lessons for practitioners and experts
The decision underscores several practical principles:
Quantum experts must independently verify quantities
Adoption of contractor-provided figures without testing exposes the evidence to rejection.Underlying workings must be produced
Summary schedules are not enough; the Court must be able to follow the chain of calculation.Methodology must be explained
The expert must articulate how quantities were measured and why that method is reliable.Proof comes before opinion
Expert opinion cannot substitute for missing factual evidence.
The lesson is that QS valuation is not free standing. It must follow the contract. Industry practice or professional preference cannot override the agreed valuation mechanism.
Lucas Earthmovers serves as a reminder that quantum evidence is not merely a matter of expertise but of proof. Courts expect quantity surveyors to do the work the role implies: measure, test, verify and explain. Where those steps are skipped, even experienced experts may find their evidence given little or no weight — or worse, treated as insufficient to establish the claim at all.
At Accura Consulting, our team of experts work with clients to create a tailored solution to problems. If you have an issue and want expert support, get in touch.
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