🪞 Cognitive Biases

What you’ll learn

1. A Bias Is the Shadow of a ShortcutDefine a cognitive bias as the predictable failure mode of a heuristic that is usually useful, and explain why this framing — rather than 'the mind is broken' — is the accurate one.A heuristic is a mental shortcut that trades accuracy for speed and usually wins that trade; a bias is what the shortcut produces in the specific circumstances where the trade fails. Because biases are the price of a working system rather than defects bolted onto it, they cannot be removed by deciding to be smarter — a framing that determines everything else in this course. The popular 'System 1 and System 2' shorthand is a useful metaphor, not two places in the brain.
2. Anchoring: The Bias That Survived EverythingDemonstrate the anchoring effect, explain why it is one of the best-replicated findings in judgement research, and identify where it operates in real life.Anchoring — the tendency for an arbitrary number to drag a subsequent estimate toward it — is unusual among biases in that it is large, easy to demonstrate, and replicates robustly, including across 36 samples and 6,344 participants in the Many Labs 1 project, where the Mount Everest item produced an effect of d = 2.23. It works even when the anchor is transparently random and even when people are warned about it. It is the mechanism underneath list prices, opening offers and salary negotiations.
3. Availability: What Comes to Mind Is Not What Is CommonExplain the availability heuristic, show how memorability rather than frequency drives risk judgement, and connect it to how news coverage systematically distorts fear.The availability heuristic substitutes ease of recall for actual frequency, which works because common things are usually easy to recall — and fails whenever something is memorable for another reason, such as being vivid, recent, or newsworthy. The systematic consequence is that dramatic rare risks feel common and undramatic common risks feel rare. Because news is by definition a selection of the unusual, an accurate picture of the world cannot be assembled from it.
4. Base Rates: The Error That Costs the MostExplain base-rate neglect using a worked medical-test example, show why the conjunction fallacy follows from representativeness, and present the frequency-framing critique honestly.Base-rate neglect — ignoring how common something is when judging how likely a case is — produces the largest practical errors of any bias in this course, as a worked example of a 99%-accurate test for a rare condition shows. The related conjunction fallacy (the Linda problem) shows resemblance overriding logic, though violations drop from a median of 87% to a median of 17% when the question is rephrased in frequencies, which is a real and instructive qualification rather than a refutation.
5. Confirmation Bias: Looking Only Where the Answer Would Please YouExplain confirmation bias via Wason's 2-4-6 task and the selection task, and show why seeking disconfirmation is both the correct strategy and psychologically unnatural.Confirmation bias is the tendency to seek and weigh evidence that would confirm a hypothesis rather than evidence that could refute it — demonstrated cleanly by Wason's 2-4-6 task, where people test only sequences their rule permits and so never discover it is wrong. The selection task shows the same structure: two of 48 solved the abstract version in one study, against 74% on a logically identical problem about drinking age, which reveals that the failure is not a general inability to reason.
6. Framing and Loss: The Same Fact, Two DecisionsDemonstrate the framing effect, explain prospect theory's account of losses looming larger than gains, and present the live scientific dispute over loss aversion honestly.Logically equivalent descriptions of the same outcome reliably produce different choices — 'saves 200 of 600' versus '400 die' flips risk preferences — and framing replicated robustly in Many Labs 1. The standard explanation is prospect theory's loss aversion, but the claim that losses loom roughly twice as large as gains is now genuinely contested, with critics arguing the evidence is weaker than its textbook status implies. The framing effect itself is not in dispute.
7. Overconfidence and Hindsight: The Two That Hide the OthersExplain calibration and overconfidence, show how hindsight bias erases the memory of uncertainty, and connect them as the mechanism that prevents learning from error.Overconfidence is the systematic gap between how sure people are and how often they are right, measurable by calibration and largest where knowledge is thinnest: answers backed at odds of a million to one prove right about nine times in ten. Hindsight bias then rewrites memory so that known outcomes feel as though they were foreseeable, which destroys the feedback that would otherwise correct overconfidence. Together they form a closed loop that explains why experience alone often fails to improve judgement.
8. The Honest Ledger: Which of These Actually ReplicateSort the biases in this course by evidentiary strength, and explain why an accurate account of a field must include what it got wrong.Judgement and decision research came through psychology's replication crisis in better shape than social psychology, but not untouched: anchoring, framing, the conjunction fallacy, base-rate neglect and hindsight bias all hold up, while priming-based effects failed and loss aversion's general form is contested. Presenting a curated list of biases as uniformly settled would repeat the exact error that caused the crisis, which is why the ledger belongs in the course rather than in a footnote.
9. The Bias Blind Spot, and What Actually WorksState the bias blind spot finding, explain why awareness is a poor defence, and assemble the procedural fixes — outside view, premortem, written predictions, frame-flipping — that do work.Asked across fourteen biases, 85% of 661 people come out reliably less biased than the average American and exactly one comes out reliably more so (Scopelliti et al. 2015), while the original and much smaller Pronin study shows the asymmetry disappearing for shortcomings people can feel operating — a finding that applies to the reader of this course with particular force. Because biases operate below introspective access, awareness is a weak defence and can backfire by supplying a vocabulary for diagnosing others. What works is procedural: taking the outside view, running premortems, writing predictions down, and flipping frames before deciding.

Questions this course answers

Grounded in trusted sources

• Tversky & Kahneman, 'Judgment under Uncertainty: Heuristics and Biases', Science 185 (1974)
• Tversky & Kahneman, 'The framing of decisions and the psychology of choice', Science 211 (1981)
• Tversky & Kahneman, 'Extensional versus intuitive reasoning: The conjunction fallacy in probability judgment', Psychological Review (1983)
• Klein et al., 'Investigating Variation in Replicability: A Many Labs Replication Project', Social Psychology 45 (2014)
• Pronin, Lin & Ross, 'The Bias Blind Spot', Personality and Social Psychology Bulletin (2002)
• Wason, 'On the failure to eliminate hypotheses in a conceptual task', Quarterly Journal of Experimental Psychology (1960)
• Griggs & Cox, 'The elusive thematic-materials effect in Wason's selection task', British Journal of Psychology 73 (1982)
• Fischhoff, 'Hindsight ≠ Foresight', Journal of Experimental Psychology: Human Perception and Performance (1975)

Every Wunder lesson is built from real, reputable sources — never invented.

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