Insights
When Expert Evidence Goes Wrong – The 5 Common Mistakes – Part 4
Part 4: The Report That Cannot Be Tested
A strong expert report should allow the reader to understand not only what the expert thinks, but how the conclusion was reached. That sounds obvious, yet many reports present opinions without making the reasoning sufficiently visible. The result may be technically impressive but difficult for the court, opposing expert or counsel to test.
The reasoning must be visible
Experience may explain why the expert is qualified to give an opinion, but it does not remove the need to show the reasoning behind it. The report should identify the evidence relied upon, the assumptions made and the analytical steps that lead from one to the other. If the reader cannot see how the expert moved from the evidence to the conclusion, the opinion becomes difficult to test.
The reasoning should also be followable by someone who does not share the expert’s specialist background. The purpose of the report is not to demonstrate the expert’s technical knowledge, but to communicate that knowledge clearly enough for the court to understand and assess it.
Assumptions, sources and models
Expert opinions frequently depend on assumptions. Some will be supplied by the instructing lawyers because the underlying facts remain disputed. Others may arise from incomplete records or from the expert’s own interpretation of the evidence. There is nothing wrong with using assumptions, provided they are clearly identified.
Problems arise when an assumption becomes embedded in the analysis and is later presented as if it were an established fact. The report should make clear which conclusions depend on particular assumptions and, where material, what would change if the court does not accept them.
The same applies to source material, calculations and models. A reader should be able to identify the evidence supporting a material conclusion without having to reconstruct the expert’s work. Where an opinion relies on certain documents, data, valuations, calculations or market information, the report should identify them sufficiently for another competent expert to understand the basis of the opinion.
If the conclusion depends on a model or numerical analysis, the methodology, important inputs and material judgements should also be explained. Complexity does not itself make an analysis persuasive.
Alternative explanations
A testable report should engage with reasonable alternative explanations. Where more than one interpretation is possible, the expert should explain why one has been preferred.
Simply stating that an alternative is “unlikely” or “not credible” is rarely enough. The court needs to understand what features of the evidence or technical analysis led to that conclusion.
A related weakness arises where the report appears to have started with the conclusion and then assembled the supporting analysis around it. This may be revealed by selective citation, unexplained assumptions or reasoning that works in only one direction.
The proper approach is the opposite. The evidence should lead to the conclusion.
A useful test is whether the reasoning would remain the same if the answer were less favourable to the instructing party.
Clear enough to be challenged
Technical language can make a report difficult to test. Specialist terminology is sometimes necessary, but it should be explained where the court may not be familiar with it. Where a simpler explanation is available without losing precision, it is usually preferable.
The report should also allow the opposing expert to understand what is being said and why. If the reasoning, data or assumptions are unclear, the experts may end up disagreeing without identifying the true source of that disagreement.
One expert may be using a different factual assumption, methodology or definition without either side recognising it. Making the analytical basis explicit can significantly narrow the issues, particularly before an experts’ meeting or joint statement.
Before finalising a report, the expert should therefore be able to answer some straightforward questions.
- Can the reader identify the evidence supporting each material conclusion?
- Are the important assumptions clear?
- Is the route from evidence to opinion visible?
- Could another competent expert understand the methodology used?
- Have reasonable alternatives been considered?
- Would the conclusion change if a key assumption were not accepted?
The value of a testable report
A testable report does not mean an unchallengeable report. Expert evidence is meant to be challenged.
The strength of the opinion lies in the fact that the reasoning can be examined and still withstand that challenge.
The court should be able to see where the evidence ends, where assumptions begin and how the expert’s expertise leads to the conclusion.
The value of an expert opinion is not simply in the answer, but in whether the reasoning allows the court to test and trust it.
srb@objectivus.com
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