The different panels show (1) the collapsed fraction of baryons, (2) the average metallicity of the IGM, (3) the volume filling factor of ionized regions, (4) the optical depth to microlensing, (5) the optical depth to electron scattering, and (6) the net damping factor for the power spectrum decomposition of CMB anisotropies as a function of the spherical harmonic index l. In this figure we examine the sensitivity of the results to changes in the normalization ﹩\sigma _{8h^{-1}}﹩ or the primordial index n of the CDM power spectrum.