Wasserstein-pp local-dependence bound for normal approximation

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Let pp be a positive integer and let W=∑i∈IXiW=\sum_{i\in I}X_i, where EXi=0{\mathbb{E}}X_i=0, EW2=1{\mathbb{E}}W^2=1, and the variables satisfy (LD1)--(LD(p+1)(p+1)): for each i1∈Ii_1\in I, i2∈Ai1,…,im∈Ai1…im−1i_2\in A_{i_1},\ldots,i_m\in A_{i_1\ldots i_{m-1}}, there is a set Ai1…im⊃Ai1…im−1A_{i_1\ldots i_m}\supset A_{i_1\ldots i_{m-1}} such that Xi1,…,Xim\\{X_{i_1},\ldots,X_{i_m}\\} is independent of Xj:j∉Ai1…im\\{X_j:j\notin A_{i_1\ldots i_m}}. Define

Rm=∑i1∈I∑i2∈Ai1⋯∑im+2∈Ai1…im+1∑(E)E∣Xi1Xi2∣(E)∣Xi3∣⋯(E)∣Xim+2∣,R_m=\sum_{i_1\in I}\sum_{i_2\in A_{i_1}}\dots\sum_{i_{m+2}\in A_{i_1\dots i_{m+1}}}\sum_{({\mathbb{E}})}{\mathbb{E}}|X_{i_1}X_{i_2}|({\mathbb{E}})|X_{i_3}|\cdots({\mathbb{E}})|X_{i_{m+2}}|,

where ∑(E)\sum_{({\mathbb{E}})} is the sum over the possible placements of E{\mathbb{E}} before each XiX_i, with any two E{\mathbb{E}}'s separated by at least two XiX_i's. Wasserstein-pp conjecture. Under these assumptions,

Wp(L(W),n(0,1))⩽Cp∑m=1p(Rm)1/m,\mathcal{W}_p(\mathcal{L}(W),n(0,1))\leqslant C_p\sum_{m=1}^p(R_m)^{1/m},

where CpC_p depends only on pp. This conjectured extension of the Wasserstein-1 normal-approximation bound concerns sums of locally dependent random variables. The case p=1p=1 was proved by Barbour, Karoński and Ruciński in 1989; the general assertion is therefore resolved at least in the stated base case, while the supplied evidence does not establish the status for every positive integer pp.

References

Primary source

Xiao Fang, “Wasserstein-2 bounds in normal approximation under local dependence”, arXiv:1807.05741 (2019).

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