Try It

Deterministic, seeded simulations you can use to test an intuition about chance before reading the explanation — every one works without JavaScript too.

• Birthday Room — How many people need to be in a room before two of them probably share a birthday? Test your intuition against an exact calculation and a simulation.
• Multiple Comparisons — Run many independent tests and watch how quickly the chance of at least one false positive climbs — even though no single test got any less reliable.
• Base-Rate Updater — See how a rare claimed ability, a good-sounding test, and a low base rate combine — most people who pass such a test still don't have the ability.
• Coincidence Generator — Generate entirely fictional synthetic lives and search them for matches — see how widening what counts as a match multiplies apparent coincidences.
• Dream Diary Test — See how often a synthetic dream diary appears to 'predict' the next day purely by chance — a methodology demo with no real dreams or diary entries involved.
• Network Crossings — A toy social-network model shows how a few random long-range connections make two 'strangers' sharing a mutual friend far less surprising.
• Runs of Heads — Predict the longest run of heads in a sequence of coin flips, then check your intuition against an exact calculation and a repeated simulation.