We propose some new two-stage stopping procedures to construct absolut
e-width and relative-width confidence intervals for a simulation estim
ator of the steady-state mean of a stochastic process. The procedures
are based on the method of standardized time series proposed by Schrub
en and on Stein's two-stage sampling scheme. We prove that our two-sta
ge procedures give rise to asymptotically valid confidence intervals (
as the prescribed length of the confidence interval approaches zero an
d the size of the first stage grows to infinity). The sole assumption
required is that the stochastic process satisfy a functional central l
imit theorem.