Confirmation bias is when an investigator searches for, or interprets, information in a way that confirms what they already believe. It’s extremely common and leads to many wrongful convictions. It’s very important to understand confirmation bias thoroughly to prevent yourself from becoming a victim of it. In this article, we’ll explain it fully and show you how to avoid it.

This article is part of our series on detective thinking. For the full framework, visit how to think like a detective.

What Is Confirmation Bias?

Confirmation bias was named and studied in detail by psychologist Peter Wason in the 1960s. In his famous “2-4-6 task” experiment, participants were told there was a hidden rule that decided which numbers belong in the sequence. Their job was to figure out the rule. To test their idea, they could create new sequences and ask if they followed the rule.

The problem was that most people only tested examples that supported their guess:

• “4, 6, 8” ✅ (confirms the rule)
• “10, 12, 14” ✅ (confirms the rule)

But they almost never tested examples that could prove them wrong:

• “1, 2, 3” ❓
• “5, 10, 15” ❓

Eventually, they discovered that the real rule was actually much simpler:

Any three numbers in increasing order.

The mistake that people made was not trying to break their own theory.

This is the basis of confirmation bias: we try to confirm our theories instead of looking for other options. It applies everywhere – in politics, in relationships, in medical diagnosis. But it is particularly bad in investigations, where the cost of reaching a wrong conclusion can mean the wrong person behind bars.

How Confirmation Bias Appears in Detective Work

Confirmation bias is very dangerous because to most people it simply feels like clear thinking. Here are the specific ways it shows up.

Selective Evidence Gathering

One of the most common things that investigators do, is to unconsciously only prioritize evidence that suits the theory they’ve already created in their head. A detective who suspects a specific person will often ask questions that illuminate that suspect’s behavior, and may not ask questions that could actually further the case.

Biased Interpretations

The same piece of evidence can be interpreted in different ways depending on whether it fits the working theory. A witness who says “I saw someone in the garden around ten” is heard as “the suspect was in the garden” by an investigator who is already convinced that someone is guilty. A better detective would use this statement to ask further questions and find out who was really in the garden.

Contradictions Being Discounted

This is when evidence that goes against a preconceived theory gets rationalized instead of investigated further.

For example: A detective is certain that a particular suspect committed a murder.

When new evidence appears, showing security footage that the suspect was somewhere else at the time of the murder, a good detective without bias might think:

“This changes everything. My theory may be wrong.”

But someone affected by confirmation bias might say:

“The camera must have the wrong time.”
“Maybe the suspect left and came back.”
“The footage is AI.”

The contradiction gets completely ignored because it goes against the detective’s original theory.

Memory Distortion

Over time, investigators can also misremember evidence in ways that favor the theory they came up with. Details that weren’t clear, get remembered as accurate and witnesses that are unreliable are remembered as reliable. When an investigator is too confident in their theory, they can remember things in a way that will confirm their bias.

Tunnel Vision

In serious real-world investigations, the most extreme version of confirmation bias is called tunnel vision. This is when an entire investigation is focused on a single suspect and all other suspects are ignored. This often happens pretty early in a case.

Tunnel vision has been responsible for lots of wrongful convictions. I’m sure you’ve seen a ton of them on YouTube or in Netflix documentaries. Investigators become invested in a theory that they’ve created, evidence is then collected and interpreted through that lens, and any evidence that contradicts that theory is ignored. The more time and resources that they spend on a particular theory, the harder it becomes for them to abandon it.

Confirmation Bias and Red Herrings

Confirmation bias and red herrings are a particularly dangerous combination. A red herring is a plausible but false lead. Someone points a finger at someone who could be guilty, and the detective just runs with it. Confirmation bias takes over completely, ignoring all new evidence and focusing only on that false lead. This leads to an investigator who isn’t just following a false lead, but is constructing a completely false theory around it.

Mystery game designers often use red herrings for just this reason. We throw a red herring into a case and let investigators create elaborate theories in their head to mislead them. Players imaginations often take hold and create their own stories around the smallest of fake details.

We cover exactly how this mechanism works in What Is a Red Herring? How Mystery Writers Use Misdirection.

How to Prevent Confirmation Bias

Confirmation bias cannot be eliminated completely, as it’s a part of human cognition, not a flaw you can simply correct for. But it can be significantly reduced. Here’s how:

Challenge your dismissed suspects. For each suspect you’ve even partially dismissed, force yourself to build the strongest possible case you can against them. If you can make a compelling case for any suspect you’d already dismissed, then you’ve dismissed them too soon.

Look for evidence that proves you wrong. Instead of asking “what supports my theory?”, ask “what would prove my theory wrong?” Then go looking for it. If you can find it and your theory still stands, it only strengthens your case. If you find it and your theory doesn’t survive, then you’ve just avoided a wrong conclusion.

Delay commitment. The longer you can hold onto multiple theories simultaneously without committing to one, the more resistant you are to confirmation bias. Once you’ve decided, the bias switches on. Hold off on a decision for as long as the evidence allows.

Bring in a second perspective. Confirmation bias is partly a social phenomenon. Shared theories can be reinforced by other members of your team. Bring in someone who isn’t part of the investigation, and who has no invested interest to the case or suspects, and they can often spot contradictions that you’ve overlooked.

Name your theory explicitly. Write it down: “I believe X did it because of A, B and C.” Making your theory explicit makes it easier to test and harder to unconsciously move the goal. When you have a vague theory, it’s way more vulnerable to confirmation bias than one that has exact points marked down.

Confirmation Bias in Murder Mystery Case Files

If you play murder mystery detective games, you’ll often spot a character that you’re certain is the killer from the onset. Sometimes you’re correct, but most good cases have multiple red herrings thrown in to keep you off-guard. Your confirmation bias is used against you to send you down the wrong path. But, if you look closer at the evidence, there’s always additional evidence that will prove that your main suspect is innocent.

One of the advantages of playing mysteries as a team exercise is that different players will form different theories, which creates natural pushback against any one person’s confirmation bias. A group dynamic can sometimes help to avoid individual tunnel vision completely.

Frequently Asked Questions

What is confirmation bias in an investigation?

Confirmation bias is when someone is so certain of their initial theory that they only seek out, and interpret, evidence to match that theory. Any evidence that goes against their theory is ignored.

How does confirmation bias lead to wrongful conclusions?

Investigators with confirmation bias dismiss evidence that contradicts their theory and continue building their false theory on additional shaky evidence. The longer is goes on for, the more confident they become in their false theory.

What is the difference between confirmation bias and tunnel vision?

Confirmation bias is when an investigator comes up with a false theory and only looks for evidence that confirms that theory, ignoring all other pertinent evidence in the process. Tunnel vision is the extreme form of confirmation bias, where an entire investigation becomes locked onto a single suspect and excludes all alternatives.

How do you overcome confirmation bias when solving a mystery?

The most effective methods are: deliberately building the strongest possible case for any suspects you’ve already partially discounted, actively looking for evidence that would disprove your theory rather than support it, delaying choosing a main suspect for as long as possible, and bringing in a fresh set of eyes into the investigation.

Is confirmation bias the same as jumping to conclusions?

They’re related but not identical. Jumping to a conclusion is a single decision made too early and on too little evidence. Confirmation bias is the sustained process that follows it. It’s the way that early conclusion now shapes all new evidence gathering and interpretation. You can jump to a conclusion without confirmation bias taking hold, but once you’ve committed to that early conclusion, confirmation bias then makes it very hard to let go of your theory even as contradicting evidence accumulates.

Confirmation Bias in Investigations

The goal in any investigation should be accuracy. Overconfidence is the enemy and will lead you to accusing the wrong people of crimes. Confidence should come from the volume of evidence you’ve collected in support of your theory, not from arrogance. And accuracy comes from the quality of how that evidence has been evaluated – including any evidence that doesn’t fit with your theories.

The best detectives are the one’s who stay curious longest. They’re the one’s willing to be wrong many times during the investigative process, and who treat their own theories with the same skepticism that they apply to suspects.

Check out our full guide on how to think like a detective for more tips. And when you’re ready to put your skills to the test, our murder mystery logic puzzles are the best place to start.