  We report a comparative study of the scattering rates using different
formalisms such as Allen\cite{allen_71}, Shulga et al.\cite{shulga_91},
Mitrovi\'c et al.\cite{mitrovic_85}, Sharapov et al\cite{sharapov_05} and
memory function formalism\cite{mori_65}. We discuss the frequency and the
temperature dependent scattering rates for the case of electron-phonon
interactions in these formalisms. The analysis has been done for different
forms of phonon density of states (PDOS) and electron density of states (EDOS).
An advantage of our study is that it shed light on the physical assumptions
used in these formalisms. From this detailed comparison, we observe that the
memory function formalism is the most general one. All other formalisms are
based on restrictive assumptions as discussed in this work.
