  A recent study of the accretion efficiency of the PG sample AGN, based on the
thin accretion disk emission model, finds the accretion radiative efficiency is
correlated with the black hole mass (eta Mbh^0.5). A followup study suggests
the correlation is an artifact induced by selection effects. Here we point out
there are two independent effects. The first is a sample selection effect,
which leads to a high L/L_Edd AGN sample. The second effect is the observed
small spread in the SED shape, which is not induced by selection effects. The
second effect is what leads to the eta Mbh^0.5 relation in the PG sample. The
physical reason for the small spread in the SED shape is an intriguing open
question.
