Short answer: almost everyone falls for some, because biases come from the fast mental shortcuts we all use, not from a lack of intelligence. Answer 9 everyday scenarios below to see which ones caught you, with a plain explanation and one habit to counter each.
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9 short scenarios. Go with your first honest answer.No sign-up; nothing is sent anywhere. About 3 minutes. Answers are revealed at the end.
The full method is in Thinking for Yourself. The book applies these habits (ask where a belief came from, ask what would change your mind, steelman before you reject) to one of the biggest inherited beliefs: religion. It argues a case for living without religion, respectfully, with the strongest opposing arguments and a reading list for both sides.
Each scenario is adapted from a classic, published experiment in judgment and decision-making (sources below). They use everyday topics (money, odds, plans, words) on purpose, so no question touches anyone's religion, politics or identity. Seven questions have a correct answer; the two factory questions are a pair, and the "trap" is only whether your choice flips when the same plan is worded as jobs saved versus jobs lost.
After the result, each bias comes with one habit to counter it. They are the habits of a mind that thinks for itself, from Thinking for Yourself, Part 10 "Doubt as a Method":
Ask where a belief came from before asking whether it's true. Beliefs that arrived by inheritance, authority or comfort need more scrutiny, not less.
Ask what would change your mind. A belief with no answer is a loyalty, not a belief.
Steelman before you reject: state the other view so well its holders would agree with your summary.
Separate the claim from the people. A claim can be wrong and the people who hold it good.
Hold conclusions provisionally, so you can update them.
Techniques from the book behind this tool
This tool puts a few of the named techniques from Thinking for Yourself to work. Each line says how it relates to the tool.
Doubt as a method: The habits given with each bias come from the book's Part 10, "Doubt as a Method".
Ask what would change your mind: One of the counter-habits the result suggests: name the evidence that would change your answer.
Steelman before you reject: State the other view so well its holders would agree with your summary before you reject it.
Separate the claim from the people: A claim can be wrong and the people who hold it good; judge them separately.
What would count as evidence: Looking for evidence that could prove you wrong is the counter to confirmation bias.
What keeps beliefs in place: community, ritual, fear, confirmation: Confirmation is one of the biases the quiz tests, and one of the book's four things that keep beliefs in place.
How beliefs get installed: "Ask where a belief came from" is the first habit; the book explains how beliefs arrive by inheritance, authority or comfort.
A systematic pattern in how people judge and decide, where a fast mental shortcut gives a predictable wrong answer in certain situations. Biases are not stupidity: the same shortcuts are usually useful, which is why everyone has them.
Which cognitive biases does this test check?
Eight well-studied ones: confirmation bias, base-rate neglect, the sunk-cost fallacy, the conjunction fallacy, the gambler's fallacy, the availability heuristic, the framing effect, and the quick intuitive answer measured by the bat-and-ball problem.
Is this an intelligence test?
No. It's a self-check on thinking habits. Missing some of these puzzles is normal; they were designed to catch the fast, intuitive thinking everyone uses. The point is to see where slowing down pays off.
How can I reduce cognitive bias?
Knowing a bias's name helps a little; changing the way you look at a problem helps more. Turn percentages into counts of real things (Gigerenzer and Hoffrage found people reason far better with natural frequencies), look for evidence that could prove you wrong, restate choices both ways, and check instant answers once.
What is confirmation bias, with an example?
Looking for evidence that fits what you already think, and not for evidence that could prove it wrong. In Wason's card task, most people turn over the card that could confirm the rule instead of the card that could break it.
Does this check judge any belief or group?
No. Every scenario is neutral and everyday on purpose. Biases are universal: they show up in every group, profession and worldview, including the one you and we hold.
Sources
Frederick, S. (2005). Cognitive reflection and decision making. Journal of Economic Perspectives, 19(4). doi:10.1257/089533005775196732 (bat and ball)
Wason, P. C. (1968). Reasoning about a rule. Quarterly Journal of Experimental Psychology, 20(3). doi:10.1080/14640746808400161 (card task)
Gigerenzer, G., & Hoffrage, U. (1995). How to improve Bayesian reasoning without instruction: Frequency formats. Psychological Review, 102(4). doi:10.1037/0033-295X.102.4.684 (base rates)
Arkes, H. R., & Blumer, C. (1985). The psychology of sunk cost. Organizational Behavior and Human Decision Processes, 35(1). doi:10.1016/0749-5978(85)90049-4
Tversky, A., & Kahneman, D. (1983). Extensional versus intuitive reasoning: The conjunction fallacy in probability judgment. Psychological Review, 90(4). doi:10.1037/0033-295X.90.4.293
Tversky, A., & Kahneman, D. (1971). Belief in the law of small numbers. Psychological Bulletin, 76(2). doi:10.1037/h0031322 (gambler's fallacy)
Tversky, A., & Kahneman, D. (1973). Availability: A heuristic for judging frequency and probability. Cognitive Psychology, 5(2). doi:10.1016/0010-0285(73)90033-9
Tversky, A., & Kahneman, D. (1981). The framing of decisions and the psychology of choice. Science, 211(4481). doi:10.1126/science.7455683
Education only. This self-check is not a psychological assessment and doesn't measure intelligence or judge any belief.