The discrepancy between Einstein mass and dynamical mass for SIS and
  power-law mass models
  We investigate the discrepancy between the two-dimensional projected lensing
mass and the dynam- ical mass for an ensemble of 97 strong gravitational
lensing systems discovered by the Sloan Lens ACS (SLACS) Survey, the BOSS
Emission-Line Lens Survey (BELLS), and the BELLS for GALaxy-Ly{\alpha} EmitteR
sYs- tems (BELLS GALLERY) Survey. We fit the lensing data to obtain the
Einstein mass, and use the velocity dispersion of the lensing galaxies provided
by the Sloan Digital Sky Survey (SDSS) to get the projected dynamical mass
within the Einstein radius by assuming the power-law mass approximation. The
discrepancy is found to be obvious and quantified by Bayesian analysis. For the
singular isothermal sphere (SIS) mass model, we obtain that the Einstein mass
is 20.7% more than the dynamical mass, and the discrepancy increases with the
redshift of the lensing galaxies. For more general power-law mass model, the
discrepancy still exists within 1{\sigma} credible region. The main reason of
the the discrepancy could be mass contamination, including all invisible masses
along the line of sight. In addition, the measurement errors and the
approximation of the mass models could lead to part of the discrepancy.
