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Data & numbers

False Alarms: Why a Positive Test Isn't What You Think

A positive test for a rare thing is usually a false alarm — count your way to the real answer, understand screening, and ask the three questions of any alarm.

6 parts 21 min total Beginner friendly Updated Aug 2026
Read Part 1 free

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What you'll walk away with

The 2%-not-95% surprise: base rate neglect, why most doctors fail the famous puzzle, and why you won't.
The counting recipe: crowd, true cases, false alarms, divide — Bayes on a napkin, no formulas anywhere.
Where it governs your life: screening callbacks, fraud alerts, drug tests, spam filters — and the tuning dial every alarm system trades on.
The second test and the three questions: how confirmation transforms the odds, updating like an adult, and the frequency scripts for the doctor's office.

6 parts · 21 min

1
The Most Counterintuitive Number in Daily Life
3 min
3 min FREE
2
Counting Your Way to the Truth
5 min
5 min
3
Where Base Rates Hide in Your Life
3 min
3 min
4
Big Nets: Why More Testing Means More False Alarms
3 min
3 min
5
The Second Test, and Updating Like an Adult
3 min
3 min
6
The Three Questions: A Playbook for Alarms
4 min
4 min
Bonus: one-page cheat sheet
Every part's key points, printable — included when you unlock

Read Part 1 free — no account needed. $1 unlocks the remaining 5 parts plus the cheat sheet, forever.

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