Why do we still have a cognitive bias that makes us send innocent people to jail? – Explanations of the confirmation bias

We often have to take objective decisions, observe something in an objective manner, or give an objective opinion. However, although objectivity is often strived for, the question is: Can we ever be truly objective? The answer is no. Since we are human beings, we all suffer numerous biases, which influence our thinking and therefore diminish our objectivity (Pronin, Gilovich, & Ross, 2004).

Introducing the Confirmation Bias

Psychological research reveals that we can all fall into the trap of the so-called confirmation bias. This bias refers to seeking, interpreting, and recalling information in ways that are adherent to our pre-existing beliefs or expectations – and its main effect is that it decreases our objectivity (Nickerson, 1998; Snyder, 1981). However, in some circumstances – for instance, during a criminal investigation – full objectivity is required and expected. But, even police officers can fall prey to the confirmation bias, which may result in miscarriages of justice. Accordingly, the question arises, if being objective is so important to us, then why do we still have this confirmation bias? Before answering this question, let's first address the possible impact of the confirmation bias where objectivity is most needed – within the legal system.

Confirmation Bias in the Criminal Justice System

As mentioned above, all people experience the confirmation bias, even those who we expect to be fully objective. Indeed, evidence suggests that the confirmation bias also extends to the legal system, with interrogators, jurors, and judges being influenced by their pre-existing beliefs concerning the likelihood of the defendant’s guilt (Hill, Memon, & McGeorge, 2008; Lange, Thomas, Dana, & Dawes, 2011). Evidently, when police officers’ decisions are led by this confirmation bias, it may be detrimental to the objectivity and efficiency of a police investigation, because they may commit solely to one causal explanation of the criminal evidence.

Indeed, the confirmation bias can make police officers become fixated on a specific suspect. This, in turn, can make them not only look for and pursue evidence that incriminates the suspected person, but also give undue weight to information that confirms their former beliefs. Moreover, the confirmation bias can make police officers neglect, devalue, or explain away any information that disconfirms or puts doubts on their pre-existing beliefs (Burke, 2007; Nickerson, 1998).

All of this results in an assemblage of evidence in support of an officer’s presumptions, which then bolsters his or her confidence in that belief (Ask & Granhag, 2005). However, doing so comes at the expense of his or her objectivity as it leads to erroneous decisions. Indeed, there are numerous examples of cases where the police was convinced they had arrested the right person, despite contradicting evidence (Sheck, Neufeld, & Dwyer, 2000). In some cases (e.g., the Birmingham Six, the Guildford Four, and the Kern County child abuse cases) this even led to innocent men and women sent to prison for years before they were finally exonerated (Williamson, 2013).

Why Does Confirmation Bias Exist?

Evidently, the existence of a confirmation bias does not lead to objective decisions, and it can have tremendous consequences, especially in the criminal justice system. Since it always leads us to erroneous beliefs, it seems like we would be better off without having this bias. However, it is still around, and this suggests that there must be a functional reason to its persistence. One possible explanation for why the confirmation bias still exists is because it protects our ego. Most people do not like to find out that their initial beliefs or expectations were actually wrong. We can prevent this by searching only for evidence that supports our view. Not finding any contradicting evidence will allow us to maintain our pre-existing beliefs. As a result, our beliefs are less vulnerable to change than if we would also search for contradicting evidence (Nickerson, 1998).

Another possible explanation could be that our desire to be consistent is so strong, that it makes it difficult to evaluate new evidence concerning one of our beliefs in an objective manner. Indeed, psychologist discovered that people attach high value to being consistent, and therefore, we find it hard to change our pre-existing beliefs (Festinger, 1957; Fiske & Taylor, 1991). This is why it may be difficult for police officers to change their view about the suspect’s guilt, despite contradicting evidence. Indeed, finding evidence that conflicts with a former belief would require an officer to change his or her pre-existing belief about the suspect’s guilt. This could happen, for example by finding out that the suspect’s fingerprints do not match those found at the crime scene. By changing their beliefs they would risk losing their consistency. Accordingly, it seems easier to devalue, or simply ignore any contradicting evidence, because this would allow them to maintain their pre-existing beliefs and thereby acting consistent.


To conclude, the confirmation bias still influences our thoughts and decisions and it thereby diminishes our objectivity. The consequences of this reduced objectivity can be miscarriages of justice, with innocent people being sent to prison. Certainly, the confirmation bias is not limited to the field of criminal justice, but can have tremendous consequences in other fields as well, such as science and politics (Nickerson, 1998). Needless to say, it seems like we would be better off without this bias. However, possible explanations to why this bias still exists might be because it can protect our ego and it can help us being consistent. Perhaps, by being more aware of the existence and the pervasiveness of this bias, people may be more cautious when forming opinions, especially when it concerns important issues.


Ask, K., & Granhag, P. A. (2005). Motivational sources of confirmation bias in criminal investigations: The need for cognitive closure. Journal of Investigative Psychology and Offender Profiling2, 43-63.

Burke, A. (2007). Neutralizing Cognitive Bias: An Invitation to Prosecutors. New York University Journal of Law and Liberty, 2, 512–530.

Festinger, L. (1957). A theory of cognitive dissonance. Stanford, CA: Stanford University Press.

Fiske, S. T., & Taylor, S. E. (1991). Social cognition (2nd ed.). New York, NY: McGraw-Hill.

Hill, C., Memon, A., & McGeorge, P. (2008). The role of confirmation bias in suspect interviews: A systematic evaluation. Legal and Criminological Psychology, 13, 357-371.

Lange, N. D., Thomas, R. P., Dana, J., & Dawes, R. M. (2011). Contextual biases in the interpretation of auditory evidence. Law and Human Behavior, 35, 178-187.

Nickerson, R. S. (1998). Confirmation bias: A ubiquitous phenomenon in many guises. Review of General Psychology, 2, 175.

Pronin, E., Gilovich, T., & Ross, L. (2004). Objectivity in the eye of the beholder: Divergent perceptions of bias in self versus others. Psychological Review, 111, 781-799.

Sheck, B., Neufeld, P., & Dwyer, J. (2000). Actual innocence: Five days to execution, and other dispatches from the wrongly convicted. New York, NY: Random House, Inc.

Snyder, M. (1981). Seek and ye shall find: Testing hypotheses about other people. In E. T. Higgins, C. P. Heiman, & M. P. Zanna (Eds.), Social cognition: The Ontario symposium on personality and social psychology (pp. 277-303). Hillsdale, NJ: Erlbaum.

Williamson, T. (2013). USA and UK responses to miscarriages of justice. In J. R. Adler (Ed.), Forensic Psychology: Concepts, debates and practice (pp. 39-55). Portland, OR: Willan Publishing.