  We present a detailed analysis of the effects of photon statistics on
multi-photon ionization. Through a detailed study of the role of intermediate
states, we evaluate the conditions under which the premise of non-resonant
processes is valid. The limitations of its validity are manifested in the
dependence of the process on the stochastic properties of the radiation and
found to be quite sensitive to the intensity. The results are quantified
through detailed calculations for coherent, chaotic and squeezed vacuum
radiation. Their significance in the context of recent developments in
radiation sources such as the short wavelength Free Electron Laser and squeezed
vacuum radiation are also discussed.
