Two Ways to Think About Chance

Ask two statisticians what '30% chance of rain' means and you can get two different answers — and both are right.

• Frequentist: repeat the day a thousand times; it rains in about 300 of them. Probability is a long-run frequency.
• Bayesian: 30% is a degree of belief — how strongly the evidence (clouds, humidity, the forecast model) supports rain.

Frequency works beautifully when you can repeat the experiment — coins, dice, A/B tests. Belief covers the cases you can't rerun — 'the probability this startup succeeds' has no thousand-trial replay.