Comparing Masses in Literature (CoMaLit)-I. Bias and scatter in weak
  lensing and X-ray mass estimates of clusters
  The first building block to use galaxy clusters in astrophysics and cosmology
is the accurate determination of their mass. Two of the most well regarded
direct mass estimators are based on weak lensing (WL) determinations or X-ray
analyses assuming hydrostatic equilibrium (HE). By comparing these two mass
measurements in samples of rich clusters, we determined the intrinsic scatters,
$\sigma_\mathrm{WL}\sim$15 per cent for WL masses and
$\sigma_\mathrm{HE}\sim$25 per cent for HE masses. The certain assessment of
the bias is hampered by differences as large as $\sim$40 per cent in either WL
or HE mass estimates reported by different groups. If the intrinsic scatter in
the mass estimate is not considered, the slope of any scaling relation
`observable--mass' is biased towards shallower values, whereas the intrinsic
scatter of the scaling is over-estimated.
