Base Rate Fallacy (29 Examples + Definition)

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Practical Psychology

Have you ever jumped to conclusions, only to find out that you ignored some important basic facts? We're all guilty of it. This article will unpack a common cognitive trap we often fall into, known as the base rate fallacy.

A Base Rate Fallacy occurs when we give too much importance to specific information and ignore the general statistics or 'base rates' that should also be factored into a decision or judgment.

So, why does this happen? That's what we're here to learn. This article will explore the theory behind the fallacy, showcase a range of examples across different fields, and offer actionable advice on how to avoid making these errors.

What is a Base Rate Fallacy?

female singer

Imagine you're judging a talent show. You hear a really good singer and think, "Wow, they must have had years of training." But what if most of the people in the talent show haven't had any formal training? That's where you'd fall into the base rate fallacy trap.

In essence, a base rate fallacy happens when you focus too much on the details right in front of you and forget about the bigger picture.

Now, let's get a bit more technical. In statistics, the term base rate refers to the overall or general frequency of an event. Base rate fallacy occurs when you disregard this general statistic.

Say you're evaluating the likelihood of an event based on some specific data. But you don't think about how common or uncommon that event generally is. That's where you go wrong.

What's the big deal, you might ask? Ignoring the base rate can lead to wrong conclusions. It can impact everything from your personal decisions to high-stakes situations like healthcare and finance.

Fallacies are logical errors, usually in arguments, that people make which lead to inconsistent reasoning or incorrect answers. The base rate fallacy is a logical fallacy when it tries to convince us that the majority opinion or popular opinion is the correct answer or best despite not having relevant evidence. It's also a cognitive bias because we often do it without realizing it.

In particular, the base rate fallacy is an informal fallacy because it is the content of the argument is wrong, not the structure of the argument; if it were the structure, it would be called a formal fallacy.

In cognitive psychology, base rates refer to the underlying probabilities or statistical norms that should inform rational decision-making. Not to mention that the false positive rate is important to know too!

Experimental psychology is often impacted by the base rate fallacy because people tend to answer subjective questions in a way that is not necessarily factual based on low relevance information.

Other Names for This Fallacy

  • Base Rate Neglect
  • Base Rate Bias
  • Base Rate Error

Similar Logical Fallacies

  • Circular Reasoning - Using the conclusion as the premise, basically arguing in a circle.
  • Post Hoc Fallacy - Believing that when one event follows another, the first event must have caused it.
  • Appeal to Ignorance - Assuming something is true because it hasn't been proven false.

The term "Base Rate Fallacy" gained traction in the 1970s, largely credited to psychologists Daniel Kahneman and Amos Tversky. They included it as part of their groundbreaking work on behavioral economics and cognitive biases. This is part of the study of behavioral and brain sciences.

The name itself is pretty straightforward; it tells you that the mistake involves ignoring the "base rate" or the general statistics involved in a situation. It's a clear term that gets straight to the point: Don't forget the big picture!

29 Examples

1) College Acceptance

Suppose you're applying to a college with a 90% acceptance rate and you score higher than the average applicant on the SAT.

This is one example of people's tendency to ignore base rates. Your higher score doesn't dramatically change the already good odds of a 90% acceptance rate, where far more students than typical will gain acceptance.

2) Medical Diagnoses

sick man

You take a test for a rare disease that has a 99% accuracy rate, and the test comes back positive so you must have the disease.

The base rate for the disease is extremely low, making your positive result likely a false alarm known as a false positive. Always get tested in more than one way when making diagnoses!

3) Job Interviews

You feel you aced your job interview for a highly competitive position so believe you will get the job.

Ignoring the base rate, your great interview doesn't significantly change the prior probability odds of only 1 in 100 applicants being selected.

4) Air Travel Safety


You hear news of a plane crash and suddenly feel nervous about flying.

The base rate of plane crashes is extremely low, making your flight likely to be safe.

5) Stock Market Trends

A stock you own has gone up for five days in a row so it must keep going up.

The base rate shows that stocks go up and down all the time; past performance doesn't predict future results. Plus, there could be an alternate explanation for the continuous rise. Don't base financial decisions solely on past performance.

6) Winning the Lottery

You buy a lottery ticket because someone in your town won last year.

The base rate and probability of winning the lottery is extremely low; one local winner doesn't change those odds.

7) Sports Performance

Your favorite team wins five games in a row so you think they are unbeatable.

The base rate of winning a championship is low, even for good teams.

8) Car Reliability

used car

You buy a certain car brand because your friend never had issues with theirs.

Always check the base rate for general reliability, as one anecdote doesn't make for reliable data.

9) Natural Disasters

You move to an area that typically has a lot of earthquakes because there hasn't been an earthquake for years.

The base rate of earthquakes in that geologically active area suggests it's not as safe as you might think.

10) Online Reviews

You read a glowing review of a newly-released smartphone and decide to buy it.

A single review doesn't represent general user satisfaction; consider the base rate.

11) Dog Behavior

You meet a friendly dog of a breed reputed to be aggressive so think that the commonly held belief that the breed is aggressive must be wrong.

Ignoring the base rate of aggressive behavior for that breed could lead to incorrect assumptions.

12) Crime Rates

You hear of a crime in a neighborhood and assume it's unsafe.

The base rate may show it's generally a low-crime area.

13) Educational Success

You see a dropout become a millionaire and assume college isn't necessary for financial success.

The base rate shows that most millionaires have a degree.

14) Food Safety

You ate expired food once and didn't get sick.

Ignoring the base rate of food-related illnesses can be risky. The base rate probability suggests that you're more likely to get sick from eating expired food than not. You probably need more specific information to know why you didn't get sick this time.

15) Diet Pills

You see a testimonial that someone lost weight using diet pills and decide to try them.

The base rate shows that most people don't lose weight using diet pills alone.

16) Shark Attacks

You hear about a shark attack so avoid the ocean.

The base rate of shark attacks is incredibly low compared to other risks like drowning.

17) Job Success

You hear that a CEO wakes up at 4 a.m. every day, so assume that to be successful you also have to wake up at 4.

The base rate reveals that many successful people wake up at more typical hours.

18) Social Media Popularity

A friend gains hundreds of followers after posting daily for a month, so you think to become popular you have to post daily too.

The base rate might reveal that most popular accounts don't necessarily post that frequently.

19) Marriage Success

Your parents divorced, so you fear you're also doomed for divorce.

Marital success isn't strictly hereditary, according to the base rate.

20) Academic Scoring

You score high on a practice test and assume you'll ace the final exam.

The base rate shows that many students do well on practice tests but not on the final exam. It may also be that your individual test results were a specific case only.

21) Dating Apps

You get many matches on a dating app and think you're highly desirable.

The base rate might reveal that most people get a lot of matches initially.

22) Talent Shows

A contestant on a talent show has an amazing voice so much be a natural.

Ignoring the base rate of natural talent can lead to wrong assumptions about training.

23) Antique Valuation

You find an old item in your attic and think it must be valuable.

The base rate shows that most old items are not valuable collectibles.

24) Child Prodigies

You hear of a child prodigy and assume all children can be prodigies if pushed.

The base rate of child prodigies suggests this is not the case.

25) Climate Change

You experience a cold winter so you doubt global warming.

The base rate of increasing global temperatures tells another story. Global warming is not about the temperature increasing equally around the world, it's about the average temperature world-wide.

26) Drug Efficacy

You take a painkiller and your headache goes away, so think that painkiller was the only way to get rid of the headache.

While it might be true that the painkiller got rid of your headache, you're ignoring the base rate of self-resolving headaches. One case in a certain person, or a small number of specific cases does not prove that a painkiller will always get rid of headaches.

27) Product Durability

Your laptop breaks down within a year, so you think that brand of laptops is garbage.

Check the base rate for brand reliability before making assumptions.

28) Recreational Risks

You go skydiving once and land safely, so think skydiving must be safe.

Ignoring the base rate of skydiving accidents can lead to a false sense of security.

29) Political Opinions

You follow a social media page that supports a particular political stance, so assume that's what everyone believes.

Ignoring the base rate of diverse political opinions could lead to a skewed worldview.

The Psychological Mechanisms Behind It

When it comes to the base rate fallacy, it's often our mental shortcuts that lead us astray. Our brains are wired for efficiency, favoring quick judgments over lengthy analysis. This is known in cognitive psychology, as heuristic thinking. This usually works well for everyday decisions but can trip us up in statistical situations, like the base rate fallacy.

Additionally, we're often influenced by availability bias, which means the most recent or emotional experiences are the ones most likely to come to mind.

For example, if you hear about a plane crash, you might overestimate the risk of flying, ignoring the high base rate of safe flights. Both heuristic thinking and availability bias can blind us to the broader statistics, leading us to make errors in judgment.

We also tend to make inaccurate probability judgments. These can be based on information we deemed irrelevant or something we have a previous example of. Formally, this is called base rate neglect.

Base rate neglect is the tendency to ignore the general statistical context, relevant information, or probability in favor of specific, immediate information when making decisions.

The Impact of the Base Rate Fallacy

The base rate fallacy can have significant and far-reaching effects on your decisions and understanding of events.

For instance, in the medical field, a misunderstanding of base rates can lead to incorrect diagnoses and unnecessary treatments. This is not only costly but also emotionally taxing for those involved.

Similarly, in the legal realm, ignoring base rates can contribute to wrongful convictions. Jurors may rely too heavily on specific but rare evidence, disregarding the broader statistical context.

The fallacy can also affect personal life choices, from the investments you make to how you assess your personal safety.

In economics, ignoring base rates might make you invest in a "hot stock," disregarding that most hot stocks don't necessarily guarantee profits. These consequences often result in not just a hit to your wallet, but also increased stress and a sense of regret.

How to Identify and Counter It

Spotting the base rate fallacy in action requires a vigilant mind. First, whenever you encounter a statistical claim, pause and think about the broader context. Are you considering all the available information, or are you swayed by a compelling story or recent event?

Be aware of your cognitive biases, such as availability bias, and try to counteract them by actively seeking out the base rates for the situation at hand.

The best way to counter this fallacy is through education and practice. Familiarize yourself with the concept of base rates and how they apply in various contexts.

Probability theory is the branch of mathematics that studies the likelihood of different outcomes in uncertain situations. You can find information pertaining to the topic at hand by looking up the probability of it.

Use critical thinking tools like Bayesian reasoning, a method that helps you update the probability of a hypothesis based on new evidence. This approach will not only enhance your decision-making but also make you a more informed consumer of news, a more careful investor, and a more rational individual in various aspects of life.

Reference this article:

Practical Psychology. (2023, October). Base Rate Fallacy (29 Examples + Definition). Retrieved from

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