March 2025

Cognitive bias in forensic science – Q&A with Dr Itiel Dror

How can experts minimise cognitive bias…

Table of contents

Introduction
What is cognitive bias?
Cognitive bias in forensic science
How can expert witnesses minimise cognitive bias?

1. Introduction

Bond Solon:

Welcome, Dr Itiel. Thank you for taking the time to talk to us.

Let’s start by getting to know you. Tell us about your career as a cognitive neuroscientist and cognitive psychologist and how you came to developing this specialism.

Dr Itiel:

I was, and still am, a researcher. I study human cognition - that is, how people think, interpret information and make decisions, etc. I specialise and focus on experts (e.g., experts in forensic evidence, medical doctors and pilots), examining if and when they make mistakes.

I am most interested when hard working, dedicated and honest experts nevertheless make erroneous judgements due to the architecture of the brain and how the brain processes information.

2. What is cognitive bias?

Bond Solon:

Great. Now, let’s go back to basics. In its simplest form, what is cognitive bias and where does it originate from?

Dr Itiel:

Cognitive bias is when what we see, and how we perceive and interpret evidence, highly depends on what we expect or hope. It is unintentional, without awareness, and we have no control over it. In everyday terms it is ‘wishful thinking’ or ‘self-fulfilling prophecies’. There are eight sources of cognitive bias, which are summarised in my article, ‘Cognitive and Human Factors in Expert Decision Making: Six Fallacies and the Eight Sources of Bias’.

3. Cognitive bias in forensic science

Bond Solon:

Your decades long research in forensic science has led you to become a pioneer in the theory of cognitive bias and how it has the potential to contaminate forensic evidence at a subconscious level. We understand that this was initially met with some outrage in a community that tended to have a “bias blind spot” but has gradually become accepted as fact.

Can you tell us about the scientific experiments and research that led you to draw these conclusions and the consequences for the forensic science community, and the criminal justice system?

Dr Itiel:

When we first started researching bias in forensic decision making, no one had even considered that forensic experts could be biased and reach erroneous conclusions –they were regarded as objective and infallible.

We kicked off our research by taking fingerprints from real cases that were ‘matched’ by fingerprint experts who concluded a 100% identification. These fingerprints were unknowingly presented to the same experts but within extraneous biasing contextual information that the prints did not match (i.e., someone else confessed to the crime). We found that many experts were biased by the irrelevant contextual information – in fact, the same expert, examining the same fingerprint evidence, reached a different conclusion. This was shocking news to the forensic and legal communities who blindly believed and accepted fingerprint evidence as objective and infallible.

We (and others) have since carried out experiments showing such bias in a whole range of forensic domains, including DNA, toxicology, forensic pathology, digital forensics, and other forensic domains. Our findings have also been corroborated by real cases where bias has been shown to impact scientific evidence, as well as judicial and scientific inquiries into forensic evidence. All of this has demonstrated that bias can play a role in forensic evidence.

4. How can expert witnesses minimise cognitive bias?

Bond Solon:

Can you tell us why it is so important that forensic scientists are aware of and accepting of cognitive bias?

And what can they do to minimise cognitive bias, particularly when they are instructed to give their opinion as expert witnesses in court proceedings, inquiries and other investigations?

Dr Itiel:

Awareness is the first step for doing something about it! When they accept the existence of cognitive bias, they can take steps to minimise bias in their work and do a better job of contributing to the administration of justice. Furthermore, accepting the existence of potential bias provides transparency and a more accurate account of what the evidence means.

It is important, for example, that experts are not exposed to irrelevant contextual biasing information and let the evidence itself (not the theory or the suspect) drive the forensic decision. Such approaches to minimise bias are called linear sequential unmasking (LSU). LSU draws upon classic cognitive and psychological research on factors that influence and underpin expert decision-making to propose a broad and versatile approach to strengthening expert decision making. It stipulates that experts should first form an initial impression based solely on the raw data/evidence, devoid of any reference material or context, even if relevant. Only thereafter can they consider what other information they should receive and in what order based on its objectivity, relevance, and biasing power.

If you would like to read more about LSU and how to apply it to improve decision making, please see my article ‘Linear Sequential Unmasking–Expanded (LSU-E): A general approach for improving decision making as well as minimizing noise and bias’.

Dr Itiel Dror is a principal consultant and researcher whose academic work relates to theoretical issues underlying human performance and cognition. He has published over 150 peer-reviewed scientific articles and is on the Board of Editors of a number of journals, including the Journal of Applied Research in Memory & Cognition (JARMAC), Science & Justice, and Pragmatics & Cognition.

If you would like to find out more information on our Expert Witness or Witness Familiarisation training, please email info@bondsolon.com or contact 020 7549 2549.