  A magnitude limited sample of nearly 9000 early-type galaxies, in the
redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey
using morphological and spectral criteria. The sample was used to study how
early-type galaxy observables, including luminosity L, effective radius R_o,
surface brightness I_o, color, and velocity dispersion sigma, are correlated
with one another. Measurement biases are understood with mock catalogs which
reproduce all of the observed scaling relations and their dependences on
fitting technique. At any given redshift, the intrinsic distribution of
luminosities, sizes and velocity dispersions in our sample are all
approximately Gaussian. A maximum likelihood analysis shows that sigma ~
L^{0.25\pm 0.012}, R_o ~ L^{0.63\pm 0.025}, and R_o ~ I^{-0.75\pm 0.02} in the
r* band. In addition, the mass-to-light ratio within the effective radius
scales as M_o/L ~ L^{0.14\pm 0.02} or M_o/L ~ M_o^{0.22\pm 0.05}, and galaxies
with larger effective masses have smaller effective densities: Delta_o ~
M_o^{-0.52\pm 0.03}. These relations are approximately the same in the g*, i*
and z* bands. Relative to the population at the median redshift in the sample,
galaxies at lower and higher redshifts have evolved only little, with more
evolution in the bluer bands. The luminosity function is consistent with weak
passive luminosity evolution and a formation time of about 9 Gyrs ago.
