  Recent work has suggested that the fraction of obscured AGN declines with
increasing luminosity, but it has been difficult to quantify this trend. Here,
we attempt to measure this fraction as a function of luminosity by studying the
ratio of mid-infrared to intrinsic nuclear bolometric luminosity in unobscured
AGN. Because the mid-infrared is created by dust reprocessing of shorter
wavelength nuclear light, this ratio is a diagnostic of f_obsc, the fraction of
solid angle around the nucleus covered by obscuring matter. In order to
eliminate possible redshift-dependences while also achieving a large dynamic
range in luminosity, we have collected archival 24 micron MIPS photometry from
objects with z~1 in the Sloan Digital Sky Survey (SDSS), the Great
Observatories Origins Deep Survey (GOODS) and the Cosmic Evolution Survey
(COSMOS). To measure the bolometric luminosity for each object, we used
archival optical data supplemented by GALEX data. We find that the mean ratio
of 24 microns to bolometric luminosity decreases by a factor of ~3 in the
L_bol=10^44-3x10^47 ergs s^-1 range, but there is also a large scatter at
constant L_bol. Using radiation transfer solutions for model geometries, we
show how the IR/bolometric ratio relates to f_obsc and compare these values
with those obtained obtained from samples of X-ray selected AGN. Although we
find approximate agreement, our method indicates somewhat higher values of
f_obsc, particularly in the middle range of luminosities, suggesting that there
may be a significant number of heavily obscured AGN missed by X-ray surveys.
