Weak law without an absolute first moment
ID: weak-law-without-an-absolute-first-moment
Let have a symmetric probability distribution with for , mass at zero, and no mass with . Then , but independent copies satisfy the weak law of large numbers with limit zero. Indeed . Their symmetric truncations have mean zero and second moment , so Chebyshev's inequality gives in probability. A union bound shows that the original and truncated sums differ with probability tending to zero. This also gives a differentiable characteristic function at zero whose derivative cannot be interpreted as an absolutely convergent expectation.
New to topics? Read the docs here!