  Using microlensing measurements from a sample of 27 image-pairs of 19 lensed
quasars we determine a maximum likelihood estimate for the accretion disk size
of an {{\em}average} quasar of $r_s=4.0^{+2.4}_{-3.1} $ light days at rest
frame $<\lambda>=1736$\AA\ for microlenses with a mean mass of
$<M>=0.3M_\odot$. This value, in good agreement with previous results from
smaller samples, is roughly a factor of 5 greater than the predictions of the
standard thin disk model. The individual size estimates for the 19 quasars in
our sample are also in excellent agreement with the results of the joint
maximum likelihood analysis.
