Should physicians think “unconsciously”?


Miguel A. Vadillo joined University College London in 2012 as a research associate after working more than ten years at the University of Deusto. Currently, he is a lecturer in decision psychology at the Department of Primary Care and Public Health Sciences, King’s College London. He also remains affiliated with UCL as an honorary research associate and collaborate with the University of Málaga as an external lecturer in the Psychology PhD programme.

Should physicians think “unconsciously”
Gregory House MD (played by Hugh Laurie) letting his brain think unconsciously about a patient diagnostic. | Credit: NBC/Universal Television

It has become almost impossible to open a popular psychology book without coming across one or several chapters about the role of intuition and unconscious processes in decision making. If you haven’t heard about the “fast” System 1 1, “gut feelings” 2 or decisions made in a “blink” 3, it might be difficult to beat your friends next time you play a trivia game.

A common topic of this literature is that many of our daily decisions are based on automatic cognitive processes that we can hardly control and that remain out of consciousness. Some authors go one step further and suggest that, in fact, unconscious processes usually outperform deliberate thinking. Perhaps you have already heard that you should rely on your “gut feeling” when making complex financial decisions, like how to invest your savings. What you probably didn’t know is that some scholars are also starting to advise physicians to rely on their intuition to make better diagnoses.

Much of the enthusiasm for these ideas stems from research on a popular phenomenon known as Unconscious Thought (UT) Effect or deliberation without attention 4. In these experiments, participants are asked to make a difficult decision like, for example, choosing among several cars on the basis of a long list of features (i.e., price, safety statistics, mileage, and so on). After receiving all this information, one group of participants (those allocated to the conscious thought condition) are given some extra time to think about all the information they have been presented with. However, participants allocated to a second group (the UT condition) are asked to spend the same amount of time performing a cognitively demanding distraction task, usually solving word-search puzzles.

You would probably expect that people who are given the opportunity to engage in conscious deliberation should make better decisions than participants who were distracted with the word-search puzzles. In contrast to this, the striking result of these experiments is that people in the UT condition usually make much better decisions than participants in the conscious thought condition, particularly when the decision is too complex to handle all the information at a conscious level.

If you think that the UT effect is too good to be true, you might be right. An increasing number of published studies have failed to replicate this effect, and the last systematic review that has explored this literature has concluded that the UT effect is not reliable 5. However, this controversy hasn’t prevented other authors from suggesting that UT might improve medical decisions. This recommendation is actually supported by some empirical evidence. For instance, an experiment found that clinical psychology students made better diagnoses after a period of distraction than after an equivalent interval of conscious deliberation 6.

However, all the other studies that have explored this issue have found either no advantage for unconscious thinking or a pattern of results that is difficult to accommodate under the standard theory of unconscious thinking. For example, Mamede and colleagues 7 found that some clinicians made better decisions after a period of distraction, but this only happened for simple medical problems, while UT theory suggests that unconscious thinking should make a critical contribution in complex problems 8. Other experiments have found absolutely no evidence for a UT advantage in medical decisions 910.

Based on this contradictory evidence, is it wise to advise physicians to make decisions based on “unconscious thought”? Whenever the results of different studies disagree, the best way to synthesize them is to conduct a meta-analysis, which allows researchers to collate the evidence for an effect provided by multiple studies and arrive at a single estimate of that effect’s magnitude.

Using this procedure, we have recently reviewed all the evidence about the contribution of unconscious thought to medical decision-making and found that the effect is unreliable 11. In fact, using an increasingly popular statistical tool known as the Bayes Factor 12 we have also confirmed that most of the experiments conducted so far reflect a genuine lack of effect of unconscious thought. This means that the failure of most experiments to find support for the UT effect is not due to a simple lack of statistical power (e.g., it is unlikely that the effect would have been significant even if these experiments had included more participants).

Therefore, unless future research shows otherwise, there is no reason to suggest that physicians would make better decisions if they spent some time “thinking unconsciously” about their patients.


  1. Kahneman, D. (2011). Thinking, fast and slow. New York: Farrar, Straus and Giroux.
  2. Gigerenzer, G. (2007). Gut feelings: The intelligence of the unconscious. New York: Viking Press.
  3. Gladwell, M. (2005). Blink: The power of thinking without thinking. New York: Little, Brown and Company.
  4. Dijksterhuis, A., Bos, M. W., Nordgren, L. F., & Van Baaren, R. B. (2006). On making the right choice: The deliberation-without attention effect. Science, 311, 1005-1007.
  5. Nieuwenstein, M. R., Wierenga, T., Morey, R. D., Wicherts, J. M., Blom, T. N., Wagenmakers, E.-J., & van Rijn, H. (2015). On making the right choice: a meta-analysis and large-scale replication attempt of the unconscious thought advantage. Judgment and Decision Making, 10, 1-17.
  6. de Vries, M., Witteman, C. L. M., Holland, R. W., & Dijksterhuis, A. (2010). The unconscious thought effect in clinical decision making: An example in diagnosis. Medical Decision Making, 30, 578-581.
  7. Mamede, S., Schmidt, H. G., Rikers, R. M. J. P., Custers, E. J. F. M., Splinter, T. A. W., & van Saase, J. L. C. M. (2010). Conscious thought beats deliberation without attention in diagnostic decision-making: At least when you are an expert. Psychological Research, 74, 586-592.
  8. Dijksterhuis, A., & Nordgren, L. F. (2006). A theory of unconscious thought. Perspectives on Psychological Science, 1, 95-180.
  9. Bonke, B., Zietse, R., Norman, G., Schmidt, H. G., Bindels, R., Mamede, S., & Rikers, R. (2014). Conscious versus unconscious thinking in the medical domain: the deliberation-without-attention effect examined. Perspectives in Medical Education, 3, 179-189.
  10. Woolley, A., Kostopoulou, O., & Delaney, B. C. (in press). Can medical diagnosis benefit from “unconscious thought”? Medical Decision Making.
  11. Vadillo, M. A., Kostopoulou, O., & Shanks, D. R. (2015). A critical review and meta-analysis of the unconscious thought effect in medical decision making. Frontiers in Psychology, 6, 636.
  12. Rouder, J. N., Speckman, P. L., Sun, D., & Morey, R. D. (2009). Bayesian t tests for accepting and rejecting the null hypothesis. Psychonomic Bulletin & Review, 16, 225-237.

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  • I find that there is a repetition by joining these two terms unconscious and thought.

  • […] ¿Qué es mejor pensar y repensar conscientemente todos los datos para llegar al diagnóstico de un paciente o dedicarse a otra cosa no relacionada y dejar que sea tu inconsciente el que diagnostique? Miguel A. Vadillo puede que tenga […]

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