TheoremBase

The Earlier and the New Versions of the Definitions of Probability Spaces, Laws, Expectation, Independence and Modes of Convergence Agree

The re-versioned definitions of probability spaces, random elements, laws, expectation, independence and the modes of convergence of random elements define the same notions as their earlier versions.

Statement

In the setting of Probability Spaces: Notation.

Probability spaces and random elements. For every measurable space (Z,A)(Z,\mathcal{A}) and every measure μ\mu on it, (Z,A,μ)(Z,\mathcal{A},\mu) is a probability space in the earlier version if and only if it is a probability space in the new version. The two versions give the same events of (Ω,F,P)(\Omega,\mathcal{F},P) (Probability Spaces, Events and Random Elements (ii)); and for every metric space (S,d)(S,d) and every n∈Nn\in\mathbb{N}, a map X:Ω→SX:\Omega\to S is a random element of (S,d)(S,d) in the earlier version if and only if it is a random element of (S,d)(S,d) in the new version, a map X:Ω→RX:\Omega\to\mathbb{R} is a random variable in the earlier version if and only if it is a random variable in the new version, and a map X:Ω→RnX:\Omega\to\mathbb{R}^{n} is a random vector in Rn\mathbb{R}^{n} in the earlier version if and only if it is a random vector in Rn\mathbb{R}^{n} in the new version.

Laws. For every metric space (S,d)(S,d) and every random element XX of SS, the law of XX in the earlier version is its law in the new version; and for every probability space (Ω′,F′,P′)(\Omega',\mathcal{F}',P') and every random element YY of SS on it (in either version, by (i)), XX and YY are identically distributed in the earlier version if and only if they are identically distributed in the new version.

Expectation. For all n,p,q∈Nn,p,q\in\mathbb{N}, the earlier and the new version give the same expectation EX\mathbb{E}X of every X∈M+(Ω,F)X\in\mathcal{M}^{+}(\Omega,\mathcal{F}) (Expectation (i), Expectation (i)) and of every X∈L1(P;Rp×q)X\in\mathcal{L}^{1}(P;\mathbb{R}^{p\times q}) (Expectation (iv), Expectation (iv)); and a random variable, or a random vector in Rn\mathbb{R}^{n}, is integrable in the earlier version if and only if it is in the new version, with the same expectation (Expectation (ii), Expectation (ii); Expectation (iii), Expectation (iii)).

Independence. For every set JJ, a family (Aj)j∈J(A_{j})_{j\in J} of events is independent in the earlier version if and only if it is in the new version (Independence of Events and of Random Elements (i)); and for every family ((Sj,dj))j∈J((S_{j},d_{j}))_{j\in J} of metric spaces and every family (Xj)j∈J(X_{j})_{j\in J} in which each XjX_{j} is a random element of SjS_{j}, the family (Xj)j∈J(X_{j})_{j\in J} is independent in the earlier version if and only if it is in the new version (Independence of Events and of Random Elements (ii)). For all metric spaces (S,d)(S,d) and (T,e)(T,e), every random element XX of SS and every random element YY of TT, XX and YY are independent in the earlier version if and only if they are in the new version (Independence of Events and of Random Elements (iii)). For every metric space (S,d)(S,d), every random element XX of SS and every σ\sigma-algebra G\mathcal{G} on Ω\Omega contained in F\mathcal{F}, XX is independent of G\mathcal{G} in the earlier version if and only if it is in the new version (Independence of Events and of Random Elements (iv)). For every metric space (S,d)(S,d) and every sequence (Xk)k∈N(X_{k})_{k\in\mathbb{N}} of random elements of SS, (Xk)(X_{k}) is independent and identically distributed in the earlier version if and only if it is in the new version (Independence of Events and of Random Elements (v)).

Convergence in probability. For every metric space (S,d)(S,d) that is separable, in either version by The Earlier and the New Versions of the Definitions of Metric Spaces, Convergence, Continuity and Compactness Agree (ii), every sequence (Xn)(X_{n}) of random elements of SS and every random element XX of SS, (Xn)(X_{n}) converges to XX in probability in the earlier version if and only if it converges to XX in probability in the new version.

Almost sure convergence. For every metric space (S,d)(S,d), every sequence (Xn)(X_{n}) of random elements of SS and every random element XX of SS, (Xn)(X_{n}) converges to XX almost surely in the earlier version if and only if it converges to XX almost surely in the new version.

Convergence in LpL^{p}. For every k∈Nk\in\mathbb{N}, every real p≥1p\ge1, every sequence (Yn)(Y_{n}) of random vectors in Rk\mathbb{R}^{k} and every random vector YY in Rk\mathbb{R}^{k} with ∥Yn−Y∥∈Lp(P)\lVert Y_{n}-Y\rVert\in\mathcal{L}^{p}(P) for every n∈Nn\in\mathbb{N}, where ∥⋅∥\lVert\cdot\rVert is the Euclidean norm, (Yn)(Y_{n}) converges to YY in LpL^{p} in the earlier version if and only if it converges to YY in LpL^{p} in the new version.

Weak convergence. For every metric space (S,d)(S,d), every sequence (μn)(\mu_{n}) of finite measures on (S,B(S))(S,\mathcal{B}(S)) and every finite measure μ\mu on (S,B(S))(S,\mathcal{B}(S)), (μn)(\mu_{n}) converges weakly to μ\mu in the earlier version if and only if it converges weakly to μ\mu in the new version.

Convergence in distribution. For every metric space (S,d)(S,d), every sequence ((Ωn,Fn,Pn))n∈N((\Omega_{n},\mathcal{F}_{n},P_{n}))_{n\in\mathbb{N}} of probability spaces, every sequence (Xn)(X_{n}) in which each XnX_{n} is a random element of SS on (Ωn,Fn,Pn)(\Omega_{n},\mathcal{F}_{n},P_{n}), and every random element XX of SS (in either version, by (i)), (Xn)(X_{n}) converges to XX in distribution in the earlier version if and only if it converges to XX in distribution in the new version.

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