A decision-maker is not obliged to listen to anybody's opinion, and the general rule is that witnesses give facts. Expert evidence is the exception, and it is a narrow one: the field has to be a real one, the person has to be qualified in it, the opinion has to rest on a basis that can be examined, and the report has to say what that basis is. This subject sets out how an opinion qualifies, what a report must contain, and what happens when two qualified people reach opposite conclusions.
A witness may be qualified by knowledge, skill, experience, training or education, and any one of them suffices. The enquiry is whether this person knows something useful about this question, not whether they hold a particular qualification. A separate and prior question is whether the claimed field is one in which expertise genuinely exists.
An expert is paid for time and analysis, and that arrangement is normal and disclosed. Fee structures tied to the outcome are treated differently and are prohibited in some fields. The questions that carry weight concern contingency, the proportion of a witness's work from one source, and the extent of instructing-party involvement in drafting.
A usable expert report identifies the question it answers, lists the material examined, separates assumptions from findings, describes the method, shows the reasoning, states the qualifications relied on and carries the declarations the forum requires. Omissions are treated as weaknesses rather than as tidiness problems.
Expert evidence is subject to a gatekeeping decision before it is heard. The questions are whether the subject genuinely admits of expertise, whether the witness possesses it, whether the method is reliable and whether the opinion assists rather than usurping the decision-maker. Challenges have to be brought early to be decided properly.
Opinion evidence falls into two categories. Lay opinion is admissible where it is rationally based on the witness's own perception and helps the decision-maker, which covers ordinary judgments about speed, condition and identity. Expert opinion requires specialized knowledge, a reliable basis and a qualified witness, and is admitted only where it would actually assist.
Country conditions evidence describes the situation in a place, and it comes from official reporting, non-governmental organizations, academic specialists and journalism. Weight turns on the source, the currency of the material and, above all, on how closely it addresses the specific circumstances rather than the country in general.
Valuation opinions depend on a defined basis, a defined date and a set of assumptions, and each of those choices moves the number. Two valuations of the same asset that differ substantially are usually both defensible, because they answered slightly different questions. Comparing the assumptions is more productive than comparing the results.
Routine translation is an administrative requirement satisfied by a certificate. Where the meaning of a term is genuinely in dispute, the question becomes one of expertise, and it is answered by evidence about usage, register and legal effect rather than by a better certificate. The two situations call for different witnesses.
A reasoned opinion sets out the material relied on, the method applied and the steps between them, which allows a decision-maker to follow it and an opponent to test it. A bare conclusion asserts a result without a visible route. The second is weaker in practice because there is nothing in it for a decision-maker to agree with.
Competing expert evidence is resolved on reasoning rather than on credentials, because reasoning is the part a decision-maker can actually evaluate. Where two reports differ, the disagreement almost always sits in the assumptions applied, the material examined or the method chosen, and identifying which of the three is responsible narrows an apparently unresolvable clash into a specific question that somebody can answer.
Handwriting examination compares a questioned writing against samples of known origin and reports a degree of similarity. The field has been re-examined in recent decades and the strength of the conclusions it supports has narrowed. Sample quality, contemporaneity and quantity determine what any comparison can actually establish.
Clinical records are made for treatment and answer treatment questions. An instructed medical opinion is written for a proceeding and answers the proceeding's question. The two documents have different purposes, different reliability profiles and different weaknesses, and treating either as the other causes most of the difficulty.
