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Theory of Statistics - George Mason University

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where Pn is the ECDF.<br />

U(X1, . . ., Xn) = 1<br />

<br />

n<br />

1<br />

n<br />

i=1<br />

= Pn(a),<br />

Example 5.18 Gini’s mean difference<br />

Θ(P) = E(|X1 − X2|)<br />

I]−∞,a](Xi)<br />

5.2 U-<strong>Statistics</strong> 403<br />

A familiarsecond order U-statistic is Gini’s mean difference, in which h(x1, x2) =<br />

|x2 − x1|, for n ≥ 2,<br />

U = 1<br />

<br />

|Xj − Xi|. (5.36)<br />

n<br />

2<br />

i

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