Anchoring Effect
A random wheel-of-fortune spin changes your estimate of how many African nations are in the UN. The spin was meaningless. The effect was real. Why?
19746 min read
Type
Probability
Chance, conditioning, and updating on evidence.
16 entriesFilter these further →
Beginner
Ages 8+, no background needed.
The Birthday Problem
How many people must be in a room before two of them probably share a birthday? The answer is far smaller than you expect.
1939 (first published), circulating from the 1920s14 min read
The Monty Hall Problem
Three doors, one car. The host opens a losing door and offers you the swap. Does it make any difference whether you take it?
1975 (posed), 1990 (made famous)9 min read
Baader-Meinhof Phenomenon
You learn a new word. Within a week, you hear it three times. Did the world start using it when you did — or did you just stop filtering it out?
20066 min read
Bertrand's Box Paradox
You reach into one of three boxes and pull out a gold coin. The chance the other coin in that box is gold is not one half.
188910 min read
Intermediate
Curious teenagers and general adult readers.
Simpson's Paradox
A treatment does better for men, and better for women, and worse for people. None of the arithmetic is wrong.
1903 (Yule), 1951 (Simpson), 1972 (named)20 min read
The Fermi Paradox
The universe is ancient, enormous, and full of ordinary stars much like ours. So where is everybody?
1950 (Fermi's remark), 1975 (Hart's argument)22 min read
Benford's Law
Look at the first digit of every number in a newspaper. You'll see 1 far more often than 9 — and it is a mathematical law, not a coincidence.
19388 min read
The Boy or Girl Paradox
A family has two children and one of them is a boy. What are the odds the other is a girl? It depends on how you found out.
1959 (posed), 1961 (retracted in part)13 min read
The Ellsberg Paradox
You know exactly how many red balls there are, and nothing about how many are black. Does knowing more make a bet more attractive?
19617 min read
Berkson's Paradox
Two things with nothing whatever to do with each other can look strongly related — purely because of who ended up in the study.
194615 min read
Peto's Paradox
A whale has a thousand times more cells than you and lives longer. It should be riddled with cancer. It is not.
1975 (observation), 1977 (Peto's fuller statement)17 min read
Advanced
Undergraduate level in the relevant field.
The Allais Paradox
Offered the same improvement in odds twice, most people take it once and refuse it the second time. Both choices feel obviously right.
1952 (posed at the Paris colloquium), 1953 (published)22 min read
The Sleeping Beauty Problem
Woken with no memory of having been woken before, how confident should you be that the coin came up heads?
1997 (posed), 2000 (named and popularised)24 min read
The St. Petersburg Paradox
A coin-flipping game whose average winnings are infinite. How much of your own money would you actually pay to play?
1713 (posed by Nicolaus Bernoulli), 1738 (published by Daniel Bernoulli)19 min read
The Two Envelopes Problem
One envelope holds twice as much money as the other. The arithmetic says swap — then says swap back, forever.
1953 (Littlewood, crediting Schrödinger), 1989 (envelope form)19 min read