Sigma

Full definition of sigma

Noun

1. The name for the eighteenth letter of the Classical and Modern Greek, the twentieth letter of Old and Ancient.
2. (mathematics) The symbol Σ, used to indicate summation of a set or series.
3. (statistics) The symbol σ, used to indicate one standard deviation from the mean, particularly in a normal distribution.
• 2011, Paul Rincon, (bbc.co.uk) LHC: Higgs boson 'may have been glimpsed'None of the spikes seen by the experiments is at much more than the "two sigma" level of certainty.
  A level of "five sigma" is required to claim a discovery, meaning there is less than a one in a million chance the data spike is down to a statistical fluke. Note: a search of "five sigma" in Wolfram Alpha yields the fact that P(z>5) = 2.867 x 10^-7 which is less than one in a million (but not less than one in ten million).

Derived terms

• sigmalike
• within one sigma: the range from the mean, plus or minus one standard deviation, usually covering 68% of the data points in a normal distribution