  We discuss the relation between `bare' cosmological parameters as the true
spatial average characteristics that determine the cosmological model, and the
parameters interpreted by observers with a `Friedmannian bias', i.e., within a
homogeneous space geometry. We may say that the latter are `dressed' by the
smoothed-out geometrical inhomogeneities of the surveyed spatial region. We
identify two effects that quantify the difference between `bare' and `dressed'
parameters: `curvature backreaction' and `volume effect'. An estimate of the
latter is given in terms of a simple geometrical example.
