What is the role and duty of an expert witness (such as a doctor) under cross-examination?

In many civil cases, especially medical negligence claims, the court needs help from someone with specialised knowledge: a surgeon, an obstetrician, an engineer or an accountant. That person is an expert witness. This article explains the role neutrally, for doctors and other professionals who may be asked to act as experts, and for parties who want to understand how expert evidence is tested.

What is an expert witness?

Ordinary witnesses give evidence of facts they saw or heard. An expert may also give opinion evidence. Section 45 of the Evidence Act 1950 makes the opinions of persons specially skilled in matters such as science or art relevant when the court has to form an opinion on those matters.

In a medical negligence case, an expert might explain what a reasonably competent practitioner in that field would have done, whether a particular complication is a known risk, or whether earlier treatment would probably have changed the outcome. The judge decides the case; the expert helps the judge understand the technical issues.

Who does the expert owe a duty to?

To the court. Order 40A of the Rules of Court 2012 provides that an expert has a duty to help the court on matters within their expertise, and that this duty overrides any obligation to the person from whom they receive instructions or by whom they are paid.

That has practical consequences:

• the report must set out the expert's genuine, independent opinion;
• it should state the facts and assumptions the opinion is based on;
• it should mention matters that might detract from the opinion, not only those that support the instructing party;
• if the expert's view changes, for example after seeing new records, they should say so.

An expert is not an advocate. A report that reads like a submission for one side usually carries less weight.

How does the court weigh medical expert evidence?

In Malaysia, the standard of care of doctors in diagnosis and treatment has been considered by the Federal Court in Foo Fio Na v Dr Soo Fook Mun and later in Zulhasnimar bt Hasan Basri v Dr Kuppu Velumani P. In broad terms, the court looks at expert evidence about accepted practice but does not simply accept it; it examines whether the opinion is logical and defensible. This is why the reasoning behind an expert's opinion matters as much as the conclusion.

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What happens in cross-examination of an expert?

The expert's report usually stands as part of their evidence, and the other side then cross-examines. Common lines of questioning include:

1. Qualifications and experience. Whether the expert actually practises in the specific area in issue, and how recently.
2. Instructions and materials. What records the expert saw and did not see, and what assumptions they were asked to make.
3. Independence. Any relationship with the parties, and how often the expert gives evidence for one side.
4. Medical literature and guidelines. Counsel may put textbooks, journal articles or clinical guidelines to the expert and ask whether they agree.
5. The other expert's view. Whether there is a respectable body of opinion that would disagree.
6. Hindsight. Whether the expert is judging the decision by what was known at the time, not by the later outcome.

How should an expert answer?

• Stay within your field. If a question goes beyond your specialty, say so.
• Concede fair points. Agreeing that a point has merit, where it does, usually strengthens credibility.
• Distinguish fact from opinion, and say which facts you are assuming.
• Be candid about literature. If you have not read an article, say so and ask for time to read it if needed.
• Explain plainly. The judge is not a doctor; avoid unnecessary jargon.
• Do not argue the case. Leave the legal arguments to counsel.

What should an expert prepare?

• The full set of medical records and documents in the bundle, not only extracts.
• Your report, re-read carefully, with a note of any errors to correct at the start of your evidence.
• The other side's expert report and any joint statement.
• Key literature and guidelines relied on in either report.
• Your CV, accurate and current.

Common mistakes

• Overstating certainty, or expressing opinions outside one's specialty.
• Refusing to concede obvious points, which makes the expert look partisan.
• Changing opinion without explanation under cross-examination.
• Relying on incomplete records without saying so.
• Using hindsight: judging a decision by the outcome rather than by what was known then.

When to speak to a lawyer

If you are a doctor asked to give an expert opinion, or to give evidence about your own treatment of a patient, it helps to understand the procedure and your duties before you write anything. If you are a party, your lawyer will explain how expert evidence fits into your case. As a former medical officer, Dr Chee understands the position of doctors asked to explain clinical decisions in court. Chris & Partners, led by Dr Chee Hui Bing, handles medical negligence litigation. Contact us; every case depends on its facts.

Frequently asked questions

Is a treating doctor the same as an expert witness?

Not necessarily. A treating doctor usually gives evidence of what they did and observed. An independent expert gives opinion on the standard of care or causation. A treating doctor may sometimes also give opinion within their expertise.

Can an expert refuse to change their report when the instructing lawyer asks?

Yes. An expert should only change a report if they genuinely agree the change is correct.

Will the court always prefer the more senior expert?

No. The court looks at the reasoning, the evidence relied on and how the opinion holds up under cross-examination.

Can experts from both sides meet?

The court may direct experts to discuss issues and identify what they agree and disagree on. Follow the court's directions.

Is it wrong for an expert to be paid?

No. Experts are commonly paid for their time, but payment does not change their overriding duty to the court.

Sources & fact check

Legal points in this article were checked against the primary sources below. The law can change; this is general information, not legal advice.

1. Rules of Court 2012, Order 40A (expert evidence) and Order 34 (pre-trial case management), gazette text
2. Evidence Act 1950 (Act 56), including section 114A, AGC Laws of Malaysia
3. Foo Fio Na v Dr Soo Fook Mun & Anor [2007] 1 MLJ 593 (Federal Court) (reported judgment)
4. Zulhasnimar bt Hasan Basri & Anor v Dr Kuppu Velumani P & Ors [2017] 5 MLJ 438 (Federal Court) (reported judgment)

Fact-checked on 17 Oct 2026