When Expert Evidence Goes Wrong – The 5 Common Mistakes – Summary

Over the past five articles, I have looked at some of the ways expert evidence can fail even where the expert is technically strong and highly experienced.

The common theme is that expert evidence depends on much more than subject matter knowledge.

The first risk is advocacy. An expert who begins to identify too closely with the instructing party may gradually lose the distance needed to assess the evidence objectively. The issue is not whether the opinion supports the client. It is whether the opinion remains genuinely independent.

The second risk arises earlier in the process. Experts are often asked to help counsel understand complex technical issues. That can be extremely valuable, but there is a danger that preliminary views become absorbed into the case theory and ultimately into the pleadings. The expert may then find themselves supporting a case they helped construct rather than independently testing it.

The third problem is answering the wrong question. Experts can stray from technical analysis into questions of law, intention, credibility or disputed fact. The strongest expert evidence is often narrower than the expert might initially expect. Its value lies in helping the court on matters that genuinely require specialist expertise while leaving the ultimate decisions where they belong.

The fourth risk lies in the report itself. A conclusion should not simply be asserted because the expert is experienced. The evidence, assumptions, reasoning and methodology should be sufficiently clear for the court and the opposing expert to understand and test. A report that cannot be tested is difficult to trust.

The final article considered what happens after the report is served. Experts’ meetings, joint statements and cross examination all test whether the expert really understands the basis and limits of the opinion. Preparation should not be about defending every sentence. It should be about knowing which conclusions remain justified, where reasonable concessions should be made and where an opinion should change.

Taken together, these five issues point to a simple conclusion.

The expert’s role is not to win the case.

It is to provide the court with independent, properly reasoned and clearly explained assistance within the expert’s area of expertise.

Technical knowledge gets an expert into the room. Independence, discipline and judgment determine whether the evidence is actually useful once they are there.