Of all the ways an otherwise competent expert report can lose credibility under cross-examination, the failure to keep fact and opinion properly separated is among the most common — and among the most damaging, because it tends to surface not as a single flaw but as a pattern running through the entire document. This piece looks specifically at how this problem shows up in delay and quantum evidence, and how to guard against it.
Why delay and quantum analysis is especially exposed
Structural and defects experts generally work from physical evidence that is, at least in principle, directly observable: a crack, a deflection, a material test result. Delay and quantum experts work from a different kind of evidence entirely — programmes, correspondence, cost records, and progress reports that require interpretation before they can support any conclusion at all. That interpretive step is exactly where fact and opinion most easily blur-sm together.
Consider a delay expert reviewing a contractor's monthly progress report claiming a particular activity was 80% complete on a given date. Whether that percentage was actually achieved on site is a question of fact. Whether that activity was, at that point, on the critical path — and therefore whether any slippage in it caused delay to completion — is a question of professional opinion, reached by applying a chosen analytical methodology to the underlying facts. A report that treats the critical path determination as though it were simply a fact drawn from the programme, rather than a conclusion the expert has reached through analysis, misrepresents the nature of its own evidence to the tribunal.
The three categories every report should distinguish
A rigorous report keeps three categories separate and clearly labelled throughout:
- Facts within the expert's own knowledge — matters the expert has directly verified, such as findings from a site inspection or figures independently confirmed against primary source documents
- Facts the expert has been instructed to assume — matters the expert has not independently verified but has been told to treat as established for the purposes of the analysis, which must be identified explicitly as instructed assumptions rather than presented as established fact
- Opinion — the expert's professional conclusion, reached by applying expertise and methodology to the facts and assumptions above
The failure mode to watch for is opinion smuggled in as fact. A quantum expert who states that "the variation increased the contract sum by AED X" without flagging that this figure depends on a contested interpretation of the valuation clause has presented an opinion as though it were an agreed or objectively established fact. Once opposing counsel exposes that gap in cross-examination, the tribunal's confidence in the rest of the report is affected — not just the specific figure in question.
Concurrent delay: where the blurring is most consequential
Concurrent delay analysis is one of the areas of construction expert evidence most prone to this problem, precisely because the underlying facts (what happened, and when) and the opinion (whether two or more causes of delay were genuinely concurrent, and what legal or contractual consequence follows) are so easily conflated. A defensible approach:
- States plainly which delay events are established by the documentary record and which are the expert's own reconstruction based on incomplete records
- Identifies the specific methodology applied (as-planned versus as-built, time impact analysis, or another recognised approach, consistent with the frameworks discussed in the SCL Delay and Disruption Protocol) and applies it consistently rather than switching methods mid-analysis to reach a more favourable result
- Separates the technical delay analysis from any submission about legal or contractual entitlement, which is a matter for counsel, not the expert
Ranges of opinion deserve honest treatment
Where professional opinion on a technical question genuinely varies — as it often does in delay methodology, or in the valuation of loss and expense claims — the report should say so, summarise the competing approaches, and explain why the expert has reached the conclusion they have. Presenting a single, unqualified figure where reasonable experts could differ, without acknowledging that range, reads to an experienced tribunal as advocacy rather than analysis, however sound the underlying reasoning may actually be.
The practical test
A useful discipline when reviewing a draft report before it is finalised: for every substantive conclusion in the document, ask whether a reader could identify, without needing to ask, whether that conclusion is an observed fact, an instructed assumption, or the expert's own professional judgment. Where that distinction is not immediately clear from the text itself, the drafting needs further work before the report is ready to be relied upon.
Part 9 continues this theme, looking specifically at how experts should handle provisional opinions and the caveats needed when the available evidence does not permit a definitive conclusion.