# About the notation of the probability measures

About the notation of the probability measures

Our textbook uses the following notation for weak convergence of probability measure:

$\mu_{n}\overset{w}{\rightarrow}\mu$

The relationship for convengence in distribution and weak convergence of distribution'' measures.

$X_{n}\overset{\mathcal{D}}{\rightarrow}X\Leftrightarrow P^{X_{n}}\overset{w}{\rightarrow}P^{X}$.

I wonder whether $P^{X_{n}}$ and $\mu_{n}$ are the same thing, i.e. $\mu_{n}\overset{w}{\rightarrow}\mu\Leftrightarrow P^{X_{n}}\overset{w}{\rightarrow}P^{X}$

Thank you!

-
It should be since $P^{X_n}$ is a measure on the image space of $X_n$. – echoone Apr 10 '12 at 0:11
So do we have "$\mu_{n}\overset{w}{\rightarrow}\mu\Leftrightarrow P^{X_{n}}\overset{w}{\rightarrow}P^{X}$"? – user16859 Apr 10 '12 at 0:13

Yes. The reason $P^{X_{n}}$ is used is because it indicates that these are distributions of $X_n$.
(i) A sequence of probability measures $\alpha_n$ is said to converge weakly to a probability measure $\alpha$ if $\alpha_n[I] \rightarrow \alpha [I]$ for all intervals of continuity I
(ii) A sequence of probability measures $\alpha_n$ with distributions $F_n$ is said to converge weakly to a probability measure $\alpha$ with distribution $F$ if $F_n(y)\rightarrow F(y)$ for all continuity points y
Thank you. I saw this argument somewhere. So you think we have $\mu_{n}\overset{w}{\rightarrow}\mu\Leftrightarrow P^{X_{n}}\overset{w}{\rightarrow}P^{X}$ ? – user16859 Apr 10 '12 at 1:52