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Comment by lostsock | Hacker News Reader

Can someone please explain what 5 sigma signifies?

Edit: “Evidence” usually means a 3-sigma signal, which existed last December, “Proof” would be a better way to describe a 5+ sigma signal, if that’s what the combined CMS/ATLAS data shows - http://www.math.columbia.edu/~woit/wordpress/?p=4809

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5 sigma is the traditional limit of significance for new discoveries in particle physics. If you have data showing the existence of a new particle or phenomenon at 5 sigma you publish and you announce and you start saying "this thing exists" instead of "this thing may exist".

They just announced 5.1 sigma, and on a normal distribution that would mean that it is 99.999966% certain, so that there is about a one-in-three-million chance that this is due to random chance, otherwise there is some sort of excess here due to a new particle.

This physics-exchange post does a great job at explaining why 5.0 sigma is required as a threshold for discovery in particle physics,

http://physics.stackexchange.com/questions/8752/standard-dev...

5 sigmas means that a model without a Higgs would have their actual data set be 5 standard deviations out from what is expected.

That corresponds to 99.99994% confidence on a standard null hypothesis test, and is the usual threshold in physics for considering something proven.

I believe 5 sigma is the threshold for "proof" in the physics community.

99.999% confidence.

Actually, it's 99.99994% confidence (1 in 1.7 million chance of error).

> Can someone please explain what 5 sigma signifies?

It means a statistically very very significant number of physicists are getting laid tonight, around the world. ;)

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