Conditional expectation
= Conditional expectation
{title2=$\mathbb E[X\mid\mathcal G]$}
{wiki}
= Conditional expected value
{synonym}
= Conditional mean
{synonym}
For an integrable random variable $X$ and a sub-sigma-algebra $\mathcal G$, the conditional expectation $\mathbb E[X\mid\mathcal G]$ is the almost-everywhere unique $\mathcal G$-measurable integrable random variable satisfying
$$
\int_G\mathbb E[X\mid\mathcal G],d\mu=\int_GX,d\mu
$$
for every $G\in\mathcal G$.