  Recently Alard\markcite{alard1996} proposed to detect the shift of a star's
image centroid, $\delta x$, as a method to identify the lensed source among
blended stars. Goldberg & Wo\'zniak\markcite{goldberg1997} actually applied
this method to the OGLE-1 database and found that 7 out of 15 events showed
significant centroid shifts of $\delta x \gtrsim 0.2$ arcsec. The amount of
centroid shift has been estimated theoretically by
Goldberg.\markcite{goldberg1997} However, he treated the problem in general and
did not apply it to a particular survey or field, and thus based his estimates
on simple toy model luminosity functions (i.e., power laws). In this paper, we
construct the expected distribution of $\delta x$ for Galactic bulge events by
using the precise stellar LF observed by Holtzman et al.\markcite{holtzman1998}
using HST. Their LF is complete up to $M_I\sim 9.0$ ($M_V\sim 12$),
corresponding to faint M-type stars. In our analysis we find that regular
blending cannot produce a large fraction of events with measurable centroid
shifts. By contrast, a significant fraction of events would have measurable
centroid shifts if they are affected by amplification-bias blending. Therefore,
Goldberg & Wo\'zniak's measurements of large centroid shifts for a large
fraction of microlensing events confirms the prediction of Han and Alard that a
large fraction of Galactic bulge events are affected by amplification-bias
blending.
