Bystander Effect
If you collapse on a busy street, your chances of getting help may be worse than on a quiet one. Why does a crowd of witnesses make you less safe?
19688 min read
Type
Aggregation
Combining many parts, votes, or groups into one result.
25 entriesFilter these further →
Beginner
Ages 8+, no background needed.
Pareto Principle
80% of results come from 20% of effort. 80% of bugs from 20% of code. Is this a law of nature, or a coincidence with a catchy ratio?
18966 min read
The Peter Principle
Why does every organisation seem to be run by people who are bad at their jobs? Because the good ones got promoted until they weren't.
19696 min read
The Prisoner's Dilemma
Two people can each do better by betraying the other — and end up worse off than if neither of them had.
195018 min read
Ringelmann Effect
Add more people to a task and each person works harder, right? Experiments show the opposite. Why does individual effort fall as the team grows?
19136 min read
The Condorcet Paradox
A majority prefers A to B, and B to C, and C to A. Every voter was honest and nobody made a mistake.
178517 min read
The Friendship Paradox
Your friends have more friends than you do. So do mine. This is true for almost everybody, all at the same time.
199117 min read
The Abilene Paradox
Everyone at the table agreed to a trip that not one of them wanted to take. How does a group choose what every member is against?
197417 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 Paradox of Tolerance
A society that tolerates absolutely everything, including those working to end it, does not remain tolerant for long.
19458 min read
The Tragedy of the Commons
Every herder gains by putting one more animal on the shared field. The field is destroyed by people behaving reasonably.
196815 min read
Brooks's Law
A software project is six months late. You add more developers. Now it's eight months late. Why?
19756 min read
Conway's Law
Your software will look like your org chart. Not because you planned it, but because you couldn't plan it otherwise.
19685 min read
Dunbar's Number
You can maintain real relationships with about 150 people. Beyond that, a group becomes something different. Is this a law of human nature?
19927 min read
Matthew Effect
Two equally talented people start. One gets a small early advantage. Decades later, the gap is enormous. Where did the extra distance come from?
19688 min read
Metcalfe's Law
Double the users of a network and the value quadruples. This simple mathematics is why some networks become monopolies and others die empty.
19806 min read
The Paradox of Thrift
Every family starts saving more. The economy ends up with less saving. How can everyone doing the right thing produce the wrong outcome?
19367 min read
Zipf's Law
The most common English word is twice as frequent as the second. Why does language obey the same mathematical law as city populations?
19357 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
The C-value Paradox
An onion carries five times more DNA than you do. A single-celled amoeba carries a hundred times more. Nobody expected that.
1971 (named), 2001 (renamed the C-value enigma)17 min read
The Easterlin Paradox
Richer people are happier than poorer people. Yet a whole country getting richer does not seem to get happier.
197423 min read
Advanced
Undergraduate level in the relevant field.
Braess's Paradox
Add a new road to a congested city and every journey gets slower. Close the road again and the traffic speeds up.
196819 min read
The Byzantine Generals Problem
Several generals must attack together or be destroyed. They can only send messengers, and some of the generals are traitors.
198222 min read
The Productivity Paradox
Computers arrived in every office through the 1970s and 80s. Measured productivity did not move for two decades.
1987 (Solow's remark), debate ongoing17 min read
Expert
Graduate level or specialist readers.
Arrow's Impossibility Theorem
There is no fair way to turn what a group of people each want into what the group wants. This is not a complaint about politics. It is a theorem.
1950 (paper), 1951 (book), 1963 (corrected second edition)25 min read