Abstract
It is shown that, in a group sequential test about the drift θ of a Brownian motion Χ(t) stopped at time Τ, the sufficient statistic (Τ, Χ(Τ)) is not complete for θ. There exist infinitely many unbiased estimators of θ and none has uniformly minimum variance. A truncation-adaptable criterion is proposed, and the uniformly-minimum-variance estimator among all truncation-adaptable unbiased estimators is found. This estimator is identical to estimators of Ferebee (1983) and Emerson & Fleming (1990). Keywords:Brownian motion; Truncation-adaptation.

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