A growing library of statistical illusions & everyday data mistakes
Data that tells the truth. Conclusions that don't.
Each illusion here is a way for flawless arithmetic to walk you confidently to the wrong answer — explained slowly, with figures you can poke. Alongside them sit hands-on tools and longer articles.
How to read the library
Same trap, different costumes
Statistical illusions are not exotic. They decide drug approvals, court verdicts, league tables, hiring rounds and headlines — and they survive because each is built from numbers that are individually, checkably true. The lie lives in the step from number to conclusion.
The library is organised by mechanism rather than by field, because the same trap resurfaces everywhere wearing different clothes: an illusion of aggregation looks the same in a hospital and a ballpark. Each illusion opens with an interactive figure where it happens in front of you — one toggle, two honest readings. Throughout, the colour claret marks the misleading reading, and each one closes with the question that would have saved you, collected at the bottom of this page as a pocket checklist. New illusions are added as they're written; the dashed cards are next in the queue.
The tools
Play with the deceptions yourself
Five hands-on instruments for committing — and catching — statistical sleights of hand. No reading required; just poke.
The library
Ways to be honestly wrong
The full set of illusions, grouped by the mechanism that powers them. Each is a self-contained explainer with an interactive figure.
The blog
Illusions caught in the wild
Longer articles tracing these traps through real headlines, studies and markets — from bacon scares to fund backtests.
The pocket checklist
The questions that would have saved you
Each illusion is disarmed by a single question, asked before believing the number. The checklist grows with the library — memorise it and you can skip the rest of the site, though you'd miss the salmon.