  We model the chameleon effect on cosmological statistics for the modified
gravity f(R) model of cosmic acceleration. The chameleon effect, required to
make the model compatible with local tests of gravity, reduces force
enhancement as a function of the depth of the gravitational potential wells of
collapsed structure and so is readily incorporated into a halo model by
including parameters for the chameleon mass threshold and rapidity of
transition. We show that the abundance of halos around the chameleon mass
threshold are enhanced by both the merging from below and the lack of merging
to larger masses. This property also controls the power spectrum in the
nonlinear regime and we provide a description of the transition to the linear
regime that is valid for a wide range of f(R) models.
