Oral Health Group

The Effect of Cognitive Bias on Evidence-Based Decision-Making in Clinical Dentistry

August 8, 2017
by Mark Douglas, MSc, DDS

What we don’t know we believe
That is the difference between a decision that is based on knowledge and evidence, and one that is not. We like to believe that all our decisions are evidence-based when in reality they most likely are not. The material being presented in lectures and in the literature which affect our decision-making processes is most likely based on flawed research, and we are quite comfortable with it. In fact, this misinformation can become entrenched and very difficult to correct. In addition, often the parameters that we are testing with research are not the ones that really need to be tested. These oversights are largely responsible for the treatment failures that we see every day. To understand why this happens and how to correct it, we need to understand how our brains process information to arrive at a decision.

We rely on scientific research to provide us with the knowledge on which we base decisions. The scientific method was developed to provide a framework by which a researcher can draw accurate conclusions about the effect of an experimental variable but most dental studies either ignore or manipulate this process to the point where the conclusions might not be valid. BMJUpdates+ annually examines the over 50,000 publications in 120 clinical journals and they find that only about 3000 studies (or 6%) utilize adequate methods to support their conclusions.1 As a result, our knowledge base may be flawed and the dental practitioner cannot truly have confidence in most of the clinical decisions that are being made throughout the day.


We need to recognize that there is a problem. We need to seriously rethink how these studies are being performed and return to an examination of the basic biophysical properties of the somatognathic system, the materials that we use to restore it, and how those materials are utilized. We also need to teach dentists to be skeptical about everything that they learn and teach them the skills needed to critically evaluate the literature.

This article serves to outline how and why our decision-making processes are sometimes flawed. It also provides a brief review of how to find accurate, unbiased information, and how to identify biases in the literature in order to avoid errors in the decision-making process.

The Decision-Making Process
When we make decisions we utilize two systems for thinking. The first system uses the logical, rational part of our brains to analyze a problem and formulate a rational decision. These functions occur within the neocortex of our brain and we are conscious of the process, however it is slow and mentally taxing. These decisions are based upon knowledge and evidence.

The other system is fast, unconscious, and is controlled by the ancient limbic part of the brain. These gut decisions are based upon emotion, intuition, instinct, and past experience. They are responsible for most of the thousands of decisions that we make every day but are also responsible for most of the judgement errors.

We have a very strong preference for unconscious gut decisions. Decision-making is a skill that develops with time and experience. When we are young and have no experience to draw upon, decision-making is basically an emotionally-driven process. When choices unfold favourably, that behaviour is reinforced and will affect future decisions. When it does not, we hopefully learn from the mistakes so that past experience will factor into related decisions in the future. As we gain wisdom, knowledge and logic enter into the decision-making process, however cognitive shortcuts such as biases also enter into the equation and can lead us to misinterpret knowledge as we reason through problems.

The Danger of Cognitive Bias
Every decision that we make is based upon the outcome of a struggle within our minds between these two decision-making systems. Tversky and Kahneman2 studied mistakes that people make during the decision-making process and found that we tend to rely more on intuition than logic and that the errors that we make are not random. They found a pattern to these errors which are termed cognitive biases.3 These biases unconsciously distort our judgement so that we are unaware of potential failure. To date, more than 150 of these biases have been identified.

Confirmation Bias is the tendency to make decisions that support our preconceived beliefs while ignoring or discrediting those that do not. In other words, we believe what we want to believe. When faced with a choice in dentistry, we consciously attempt to utilize the logical part of our brain, but the automatic, unconscious intuitive system takes over. As a result, we interpret the evidence in such a way that we arrive at a decision that we feel is right or in other words, confirms our preconceptions. This Confirmation Bias is a potential source of judgement error. While we consciously think we are making a logical evidence-based decision, we are subconsciously making potentially flawed intuitive decision.

A Publication Bias occurs when the Confirmation Bias and other factors creep into the peer-review system of the scientific literature. When a scientific paper is submitted to a journal, it undergoes a process whereby peers review the publication to assess its accuracy, relevance and contribution to the scientific literature. Variables such as the author’s reputation and academic affiliations have a positive influence on the reviewer’s recommendation as do the reviewer’s agreement with the results. To address this bias, many journals have now blinded the review process such that the reviewer does not know the identity of the author. It has always been assumed that this process is objective and adequate but it had never been studied. In 1977, Mahoney4 examined this blinded peer-review process and found that studies which confirmed the hypothesis were much more likely to accepted for publication. In another study by Mahoney et al5, they found that authors who cited their own “in press” publications had a greater chance of having their article accepted for publication.

When a manufacturer pays for a study that evaluates their product, the results and conclusions tend to favour their product more than independently funded studies. This is a Sponsorship or Funding Bias. In a Cochrane review, Lundh et al6 examined review articles examining drugs and medical devices and found that industry sponsored studies show a bias in favour of the sponsor’s products. In addition, most articles fail to acknowledge the source of their funding leading to difficulty in evaluating whether a Sponsorship Bias is present or not. Faggion et al7 reviewed the periodontal and implant dentistry literature also found that many studies fail to disclose funding sources or the author’s conflicts of interest such as employment by, or stock ownership of the sponsoring company. At dental conventions and lectures, industry sponsorship has invaded the objective and unbiased dissemination of information. Reviewing the list of lectures and speakers for many conventions reveals the strong relationship between the dental industry and convention providers. Faggion8 examined the lecture presentations at seven dental meetings across Europe and North America and found industry sponsorship of the scientific programme but no clear guidelines for presenting research findings or disclosure of conflicts of interest. He proposes severing the industry sponsorship of scientific lectures and recommends standardized guidelines for the presentation of research findings to help eliminate bias in these presentations.

Finding Unbiased Information
Dentists typically get their information from three sources – lectures, journals, or sales representatives that work for a dental manufacturer. Dentists are very comfortable with the lecture format for gaining the information they need. A large volume of information can be assimilated in a very short period of time because the lecturer has devoted a tremendous amount of time distilling the volumes of information and may even provide references to scientific articles that support their point. So, while we think we are making a knowledge-based decision, in reality we are making a gut decision based on the trust that we place in the skill and reputation of the lecturer. The problem is, lecturers are also prone to cognitive biases and may not realize it themselves. The Authority Fallacy Bias occurs when we base our decisions on information presented by some authority as fact, however these authorities are prone to judgement errors due bias, dishonesty, or influence of Groupthink. Groupthink is a phenomenon whereby the consensus of the majority of experts is accepted as fact. However, this consensus may still be wrong. For example, before medicine was aware of the existence of bacteria, physicians believed that handwashing was unnecessary which led to countless deaths from infection. We should always question the status quo. To address these concerns, lecturers should disclose any conflicts of interest as well as provide a list of publication references to their lecture material for the attendee to critically evaluate on their own.

Sales representatives in the dental industry will also provide you with literature to read on their products however this information should be regarded with skepticism. The information they are providing you with is marketing material, not unbiased scientific proof. Any information provided, should be verified with a review of the scientific literature on the topic.

To find research articles, Internet search engines such as Google Scholar and PubMed are a good starting point. They return a comprehensive listing of articles with abstracts. Review articles can condense this large volume of information and may reveal flaws in study design, however they may also reflect the bias of the author. Some articles are available for download as full text while most are not. Full text versions can often be obtained by contacting the author for a reprint, purchasing an article online, or by searching the American Dental Association’s library of online eJournals and eBooks. ADA members have access to over 330 dental journals with thousands of full text articles available for download.

When reading scientific articles, bear in mind that biases can invade the study design and publication processes. In addition to Sponsorship Bias, factors such as small sample size, failing to control confounding variables, not identifying exclusion criteria for discarded data, or relying on anecdotes as proof compromise the quality of evidence. In 2005, John Ioannidis published a controversial landmark essay in which he developed a mathematical model to show that most medical research is flawed.9 The Cochrane Collaboration publishes review articles on many healthcare topics in an effort to provide clinicians with the information needed to make an evidence-based treatment decision. Unfortunately, there are very few dental topics covered and of those covered, most conclude that there is insufficient evidence due to poorly designed studies and a lack of double blind randomized clinical trials. Pandis et al10 reviewed articles from Cochrane and other influential dental journals and concluded that only 2% of studies that assessed interventions in dentistry were of high quality while 18% were of moderate quality raising concern that many commonly accepted interventions in dentistry are unproven.

We need to return to studying the basic biophysical principles of the somatognathic system. What are the factors that make the natural dentition so robust, what are the factors that compromise it? Biomaterials and treatment modalities need to be tested with well-designed unbiased Randomized Clinical Trials. Finally, we need to teach students and practitioners the skills needed to critically evaluate the literature in a truly unbiased manner.

This article serves to point out many of the unconscious biases that we have in making treatment decisions in dentistry. We must be aware that not only the reader, but also the researcher, author, and lecturer are prone to these same biases. Considering that the vast majority of dental literature is biased and unreliable, we cannot have confidence that the treatment decisions that we make are proven. Be skeptical and don’t believe everything that you read or are told. Only after the profession demands that researchers follow accepted, unbiased principles of study design will we be have confidence in the decisions that we make. OH

Oral Health welcomes this original article.

Acknowledgement: The author wishes to thank Dr. Bjug Borgundvaag MD, PhD, Emergency Physician, Director &
Researcher – Schwartz/Reisman Emergency Medicine
Institute for his feedback and guidance in preparing this


1. R. Brian Haynes. bmjupdates+, a new free service for evidence-based clinical practice. Evid Based Nurs 2005 (8): 39.

2. Tversky, A and Kahneman, D. Judgement under uncertainty: heuristics and biases. Science Sep 1974 185(4157): 1124-1131.

3. Kahneman, D & Frederick, S. (2002). “Representativeness Revisited: Attribute substitution in intuitive judgment”. In Thomas Gilovich, Dale Griffin, Daniel Kahneman. Heuristics and Biases: The Psychology of Intuitive Judgment. Cambridge: Cambridge University Press. pp. 51–52.

4. Mahoney, M. Publication Prejudices: An experimental study of confirmatory bias in the peer review system. Cognitive Therapy and Research 1977 1(2): 161-175.

5. Mahoney, M, Kazdin A, & Kenigsberg, M. Getting Published: The effects of self-citation and institutional affiliation. Cognitive Therapy and Research 1978 2(1): 69-70.

6. Lundh, A, Sismondo, S, Lexchin, J, Busuioc, O, and Bero, L. Industry sponsorship and research outcome. Cochrane Database Syst Rev 2012; 12: MR000033.

7. Faggion, C, Ateih, M, and Zanicotti, D. Reporting of sources of funding in systematic reviews in periodontology and implant dentistry. Br Dent J 2014 216 (3): 109–112.

8. Faggion, C.M. Are there guidelines for reporting clinical research findings in oral lectures and seminars in dental meetings? Br Dent J 2013 214(6): 281-283.

9. Ioannidis, JPA. Why most published research findings are false. PLos Med 2(8):e124.

10. Pandis N, Flemming PS, Worthington H, Salanti G. The quality of evidence according to GRADE is predominantly low or very low
in oral health systematic reviews. PLoS ONE 2015 10(7): e0131644.

Mark Douglas graduated from the University of Toronto Faculty of Dentistry in 1991 following the completion of a Masters Degree in Physiology from Queens University. He maintains a private practice in West Toronto where he has practiced for 25 years. Since graduating, he has been active in organized dentistry, serving on the Ontario Dental Association’s General Council and Education Core Committee, as well as President of the West Toronto Dental Society and the Toronto Crown and Bridge Study Club.