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Law of the Iterated Logarithm


The law of the iterated logarithm gives the almost-sure asymptotic magnitude of the fluctuations of a sum of independent random variables. If X_1, X_2, ... are independent and identically distributed with expectation value 0 and finite positive variance sigma^2, and S_n=X_1+...+X_n, then

 limsup_(n->infty)(S_n)/(sqrt(2sigma^2nlnlnn))=1,

almost surely. Applying the result to -S_n gives the corresponding infimum limit -1.

The theorem refines the law of large numbers: the latter gives the scale on which S_n/n tends to 0, while the iterated logarithm gives the precise envelope of the remaining fluctuations.


See also

Central Limit Theorem, Law of Large Numbers, Supremum Limit

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References

Durrett, R. Probability: Theory and Examples, 4th ed. Cambridge, England: Cambridge University Press, 2010.

Cite this as:

Weisstein, Eric W. "Law of the Iterated Logarithm." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/LawoftheIteratedLogarithm.html

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