A Note on the Variance of a Stopping Time
Keener, Robert
Ann. Statist., Tome 15 (1987) no. 1, p. 1709-1712 / Harvested from Project Euclid
Let $\{S_n = \sum^n_1 X_i\}_{n\geq 0}$ be a random walk with positive drift $\mu = EX_1 > 0$ and finite variance $\sigma^2 = \operatorname{Var} X_1$. Let $\tau(b) = \inf\{n \geq 1: S_n > b\}, R_b = S_{\tau(b)} - b, M = \min_{n\geq 0} S_n, \tau^+ = \tau(0)$ and $H = S_\tau +$. Lai and Siegmund show that $\operatorname{Var} \tau(b) = b\sigma^2/\mu^3 + K/\mu^2 + o(1)$ as $b \rightarrow \infty$, but give an unpleasant expression for the constant $K$. Using the identity $\int Eh(R_{-y}) dP(M \leq y) = E^+_\tau h(H)/E\tau^+$, the expression for $K$ can be simplified to a form that depends only on moments of ladder variables.
Publié le : 1987-12-14
Classification:  Random walks,  ladder variables,  stopping times,  excess over the boundary,  60J15,  60G40
@article{1176350620,
     author = {Keener, Robert},
     title = {A Note on the Variance of a Stopping Time},
     journal = {Ann. Statist.},
     volume = {15},
     number = {1},
     year = {1987},
     pages = { 1709-1712},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1176350620}
}
Keener, Robert. A Note on the Variance of a Stopping Time. Ann. Statist., Tome 15 (1987) no. 1, pp.  1709-1712. http://gdmltest.u-ga.fr/item/1176350620/