Lévy's convergence theorem

Lévy's convergence theorem

In probability theory Lévy's convergence theorem (sometimes also called Lévy's dominated convergence theorem) states that for a sequence of random variables (X_n)^infty_{n=1} where

*X_nxrightarrow{a.s.} X and
*|X_n| < Y, where "Y" is some random variable with
*mathrm{E}Y < infty

it follows that

* mathrm{E}|X| < infty,
*mathrm{E}X_n o mathrm{E} X
*mathrm{E} |X-X_n| o 0.

Essentially, it is a sufficient condition for the almost sure convergence to imply "L"1-convergence.The condition |X_n| < Y,; mathrm{E}Y < infty could be relaxed. Instead, the sequence (X_n)^infty_{n=1} should be uniformly integrable.

The theorem is simply a special case of Lebesgue's dominated convergence theorem in measure theory.

ee also

* Convergence of random variables
* Fatou's lemma

References

*A.N.Shiryaev (1995). "Probability, 2nd Edition", Springer-Verlag, New York, pp.187-188, ISBN 978-0387945491


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