So we have the jensen's inequality: $$|EX| \leq E|X|$$
Any bound on the Jensen gap (upper bound or lower bound)? $$\text{gap}=E|X| - |EX|$$
So we have the jensen's inequality: $$|EX| \leq E|X|$$
Any bound on the Jensen gap (upper bound or lower bound)? $$\text{gap}=E|X| - |EX|$$
Copyright © 2021 JogjaFile Inc.
The gap can be arbitrarily large. For instance, if $X$ is a random variable so that $X(0) = -N$ and $X(1)=N$, and the events $0$ and $1$ have probability $1/2$, then $|E(X)| = |\frac{1}{2}N - \frac{1}{2}N|=0$, but $E(|X|) = N$.