Statistics of a 'discovery'

• Particle physics has an accepted definition for a "discovery": a five-sigma level of certainty
• The number of standard deviations, or sigmas, is a measure of how unlikely it is that an experimental result is simply down to chance rather than a real effect
• Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
• The "three sigma" level represents about the same likelihood of tossing more than eight heads in a row
• Five sigma, on the other hand, would correspond to tossing more than 20 in a row
• A five-sigma result is highly unlikely to happen by chance, and thus an experimental result becomes an accepted discovery