There is an important distinction between being instructed as to the facts of a case and accepting those facts without question. It is a distinction which, in my view, goes to the very heart of the role of the Expert Witness. An expert will inevitably receive instructions setting out a client’s position, often supported by pleadings, witness statements, correspondence, schedules and selected contemporaneous records. Those materials provide the starting point for the expert’s work, but they should not necessarily provide its conclusion. The expert’s responsibility is to form their own independent opinion, and that requires more than simply analysing the material that has been placed before them.
This is particularly important in construction disputes. By the time an Expert Witness becomes involved, the dispute may already have developed over many months or even years. Positions have hardened, pleadings have been prepared and a considerable amount of work may already have been undertaken by solicitors, counsel, claims consultants and the parties themselves. The expert therefore enters an environment in which a narrative has inevitably begun to emerge. That narrative may ultimately prove to be entirely correct, but the fact that it forms part of the expert’s instructions does not relieve them of the responsibility to test the evidential foundations upon which it rests.
For me, one of the essential disciplines of expert work is therefore to maintain a clear distinction between instructions, assumptions, evidence and opinion. Instructions tell the expert what they have been asked to consider. Assumptions may provide a necessary basis upon which an opinion can initially be developed. The evidence determines whether those assumptions can ultimately be sustained, and the expert’s opinion should emerge from their independent analysis of that evidence. Problems begin to arise when those separate stages become blurred and an instructed factual proposition gradually becomes treated as though it were an established fact.
That does not mean that an Expert Witness is required to become an investigator without boundaries, nor does it give an expert licence to embark upon enquiries wholly unrelated to the issues upon which they have been instructed. The scope of the appointment remains important, as does the boundary of the expert’s own expertise. There is, however, a considerable difference between remaining properly within the scope of an instruction and failing to pursue an issue which is obviously material to the reliability of the opinion being expressed. If the expert identifies a gap in the evidence that materially affects their conclusions, it cannot in my view be sufficient simply to ignore it because the missing information was not included within the original bundle.
This issue frequently manifests itself through the contemporaneous documents. An expert may be provided with a witness statement describing what occurred on a project several years earlier, but the records produced at the time may tell a rather different story. Meeting minutes, valuations, payment notices, cost reports, instructions, programmes, emails and site records can provide an evidential picture which is considerably more nuanced than the narrative subsequently developed for the purposes of the dispute. The expert’s responsibility is not to decide whether a witness is truthful; that is a matter for the Court or Tribunal. It is, however, entirely proper for the expert to identify where the factual assumptions upon which their opinion depends are inconsistent with, or unsupported by, the contemporaneous material available to them.
Equally important is recognising what is not within the bundle. In Quantity Surveying and quantum disputes, experience will often tell an expert that certain records would ordinarily be expected to exist. If a valuation is said to have been undertaken, where is the underlying measurement? If substantial additional costs are claimed, where are the cost ledgers, invoices, allocation records or other contemporaneous records supporting them? If a particular instruction is said to have caused significant additional expenditure, what records demonstrate the relationship between the instruction and the cost claimed? The absence of such documentation does not automatically determine the issue, but it should prompt further enquiry rather than unquestioning acceptance.
In my experience, some of the most useful questions an expert can ask are therefore remarkably simple: What evidence would I expect to see if this proposition were correct? Does that evidence exist? If it does not, why not? And is there evidence elsewhere within the material that points towards a different explanation? Those questions are not designed to undermine the case of the party instructing the expert. They are designed to ensure that any opinion ultimately expressed is capable of withstanding independent scrutiny.
That distinction is important because identifying a weakness in an instructing party’s case is not a failure by the expert. Quite the opposite. An expert who identifies at an early stage that a factual assumption cannot be supported, that further evidence is required or that a particular head of claim cannot be substantiated may provide considerably greater value than an expert who simply accepts the proposition and allows the problem to emerge later. A difficult conversation with the instructing solicitor during the preparation of the report is generally preferable to the same weakness being identified for the first time by the opposing expert, an adjudicator, arbitrator or, ultimately, during cross-examination.
There is also an important relationship between investigation and independence. In earlier articles I have considered confirmation bias and the risk that prolonged exposure to one party’s narrative can gradually influence an expert’s thinking. Proper investigation is one of the practical safeguards against that risk. An expert who actively looks for evidence capable of disproving their provisional conclusion is far less likely to become unconsciously committed to it. The question should not simply be, “What supports my opinion?” It should also be, “What evidence would cause me to change it?” In my view, the second question is often the more important of the two.
Having acted as an Expert Witness and Single Joint Expert, and having considered expert evidence from the different perspective of an adjudicator, I have become increasingly conscious of the distinction between an opinion that has been genuinely investigated and one that largely reproduces the case advanced by the instructing party. From the decision-maker’s perspective, that distinction can be significant. Where an expert has identified assumptions, tested them against the available records, acknowledged evidential gaps and explained how those matters affect their conclusions, the reasoning can be evaluated. Where an expert simply adopts factual propositions provided in their instructions without demonstrating how those propositions have been tested, considerably greater caution may be required before weight can properly be placed upon the resulting opinion.
The same issue arises when I am instructed in professional negligence matters involving the work of other construction professionals. It is often tempting, particularly with the benefit of hindsight, to focus immediately upon whether the ultimate conclusion was right or wrong. I believe the more useful question is frequently whether the professional undertook a reasonable and sufficiently rigorous process before reaching that conclusion. Expert evidence should be approached in much the same way. The quality of an opinion cannot properly be separated from the quality of the investigation and analysis that produced it.
There are, of course, limits. Experts should not stray into matters of law, determine disputed questions of fact that are properly reserved for the Court or Tribunal, or extend their enquiries beyond the boundaries of their expertise. Nor should an expert attempt to assume the role of the solicitor conducting disclosure. The point is rather more straightforward. If information is material to the expert’s opinion, the expert should satisfy themselves that they have sufficient evidence upon which to express that opinion. Where they do not, the appropriate response is to request the necessary material, identify the assumption being made or explain the limitation upon the opinion. What they should not do is silently fill the evidential gap with the case advanced by those instructing them.
This is also why the obligation to investigate cannot be separated from the obligation to remain willing to change one’s opinion. Further investigation may produce evidence inconsistent with the expert’s provisional view. If it does, the proper response is not to search for a means of preserving the original conclusion but to reconsider it. An expert who investigates only until they find evidence supporting the position they have already adopted is not truly investigating at all. They are seeking confirmation.
Ultimately, an Expert Witness is instructed to provide expertise, not endorsement. The letter of instruction defines the questions that require expert consideration, but it should not dictate the answers. Those answers must emerge from the expert’s own investigation, experience, analysis and professional judgment. That may sometimes result in an opinion which strongly supports the instructing party’s case; on other occasions it may identify significant difficulties with it. Neither outcome should concern the genuinely independent expert. What matters is that the opinion expressed is the one justified by the evidence.
For that reason, when considering my own work, I increasingly return to a simple question: have I reached this conclusion because the evidence has taken me there, or because that was where my instructions started? The distinction is fundamental. The Expert Witness who investigates rather than merely accepts is not making the litigation process more difficult. They are doing precisely what they were instructed as an independent expert to do.