Medical expert witnesses: tips and traps when giving evidence

Jul 20, 2017

In the second of our two-part series, we look at the medico-legal implications of being an expert witness including key tips and traps, protecting your reputation and landmark cases. 

While being an expert witness is a professional privilege, it can be a daunting prospect for some doctors and comes with some unique pitfalls. However, our preparation guide will smooth the process.



Giving evidence: tips  


Be prepared and form your opinion  

Thorough preparation is a key part of being a credible and confident expert witness. These initial steps will help you get started:

  • Find out the date your report is due.
  • Read the relevant Expert Witness Code of Conduct.  
  • Read all the documents and the questions and identify the main issues.   
  • You may be asked to assume certain facts and events. Distinguish between background history and assumptions of fact.  Ensure that you get the facts and the assumptions correct, and in the right order.
  • Do your research before you put pen to paper.
  • Work out how you are going to explain your opinion and the reasons for your opinion.
  • Know exactly where you obtained the information in the documents for your report as you will need to refer to these later.
  • Challenge your opinion and conclusions ­– is your opinion consistent with the evidence base?

Develop clear reasoning

The reasons for any conclusions you reach and opinions you make must be clear. It’s important to link the facts and any assumptions to your opinion, and to ensure there is a logical flow between them. Do not hypothesise as to what may or may not have happened in a case. If there are any gaps in the sequence of events, check that you haven’t filled in any factual gaps with your own facts.  

If you have any concerns about your opinion, for example, based on contradictory assumptions, address these before you write your report. It’s a good idea to call the lawyer who engaged you in the case to clarify your concerns and obtain more information. 

If something is unclear, you may decide you need to give more than one opinion. For example, ‘I am unable to conclude from the documents and the assumptions provided that Dr Y warned the patient of… If he did, then my opinion is… If he didn’t, then my opinion is…’

Be clear about the limits of your knowledge, and don’t give an opinion outside your area of expertise.

Giving evidence: decision traps

When forming your opinion as an expert witness, there are a number of common traps that should be avoided. 

Contradicting what’s in your report

Firstly, if the matter goes to court, ensure that you read all the documents again, particularly all the references you have quoted. There is nothing more embarrassing than finding that counsel (or their expert) have read something you quoted that contradicts your own argument.

Outcome bias

Expert witnesses should be aware of the influence of ‘outcome bias’, which is a tendency to judge a decision on the basis of its outcome rather than on what factors led to the decision. Outcome bias can be avoided by focusing on what was reasonable at the time the event happened. The court is interested in what was competent and reasonable practice, and not was best practice.

Not recognising levels of evidence

When you are assessing a doctor’s standard of care, it’s important to keep in mind that all guidelines are based on different levels of evidence and to recognise the difference between a directive, a policy, a standard, a guideline, and a position statement.

It’s important to recognise that just because a guideline exists doesn’t mean that there is no other way to do things.

Looking backward, not forward

As the saying goes ­– hindsight is a wonderful thing. Ensure that your view isn’t coloured by the phenomenon known as ‘hindsight bias’. This is defined as predicting the probability of an adverse event retrospectively. Guard against this by putting yourself in the shoes of the doctor you are judging and look forwards, not backwards.

Advocating for the client

As an expert witness it’s easy to fall into the trap of being an advocate for the client of the lawyer who engaged you. For example, ‘It’s easy to imagine that Dr X would have insufficient time to assess Mrs X’s history, discuss the ultrasound and also examine her.’ This comment indicates that you are guessing what was in the mind of Dr X, and could be interpreted as advocacy. You may think that a few comments can’t hurt, but as an expert witness, your key role is to provide an impartial opinion to assist the court make an informed and fair decision. Courts do not take kindly to experts giving evidence which displays advocacy.       

Landmark decision removes expert witness immunity     

If you fail to take reasonable care in providing an expert opinion, you will generally not be liable for civil or criminal proceedings. However, a landmark decision of the Supreme Court of the United Kingdom has removed the protection for expert witnesses against suits by people they had instructed to provide evidence on their behalf.

It’s important to be aware of your responsibilities and mindful that an expert witness can face disciplinary action for evidence given in court which is seriously flawed.

In a case in the United Kingdom, a paediatrician gave evidence that the sudden infant deaths of two babies in the same family could not be explained by natural causes. The paediatrician used statistical research to support his opinion that the likelihood of two deaths occurring from natural causes was extremely low. It was later proved that the paediatrician had made a significant error in applying the statistics. Subsequently, the mother of the children who had been convicted of killing both children had the conviction overturned.

The paediatrician faced action by the General Medical Council to deregister him. Although he escaped deregistration, the English Court of Appeal found that expert witness immunity does not protect experts from disciplinary action for serious substandard care in giving expert evidence.

Although rare, criminal proceedings can also result if you act as an expert witness and deliberately lie in court or give an opinion you do not honestly hold.

Keep the information in mind above to ensure that your opinion is unbiased and carefully considered based on sound evidence.

More information

The Whole Truth Handbook: responsibilities when providing evidence can assist doctors in giving evidence in court. Complete the course material and receive a certificate of completion and CPD points.

Download the AMA’s Ethical Guidelines for Doctors acting as Medical Witnesses 2011. Revised 2016.  

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