We estimate the radiative efficiency \epsilon of individual type 1 SDSS QSOs by using their bolometric luminosities ( L _ { bol } ) and accretion rates ( \dot { M } _ { \bullet, acc } ) , which may be related to the assembly histories and spins of the central massive black holes ( MBHs ) .
We estimate L _ { bol } by using the empirical spectral energy distributions of QSOs and \dot { M } _ { \bullet, acc } by fitting the observed optical luminosity ( /-ies ) with the thin accretion disk model , assuming the MBH masses given by the virial mass estimator ( s ) ( M _ { \bullet, vir } ) .
We find an apparent correlation between \epsilon and M _ { \bullet, vir } , which is strong at redshift z \la 1.8 , weak at z \ga 2 , and consistent with that found by Davis & Laor ( 7 ) for 80 PG QSOs at z \leq 0.5 .
To investigate whether this correlation is intrinsic or not , we construct a mock sample of QSOs according to the true MBH mass and Eddington ratio distributions given in Kelly & Shen ( 19 ) .
By comparing the results obtained from the mock sample with that from the SDSS sample , we demonstrate that the apparent \epsilon - M _ { \bullet, vir } correlation can be produced by and mainly due to the selection effects of the SDSS sample and the bias induced by the usage of M _ { \bullet, vir } as the true MBH mass .
The mean values of \epsilon of those SDSS QSOs are consistent with being a constant \simeq 0.11 - 0.16 over the redshift range of 0.3 \la z \la 4 .
We conclude that the current SDSS QSO data is consistent with no strong intrinsic correlation between radiative efficiency and true MBH mass and no significant redshift evolution of radiative efficiencies .