In some theoretical analyses of microwave-induced magnetoresistance oscillations in high-mobility two-dimensional systems, the inelastic relaxation time $tau_{in}$ due to electron-electron scattering is evaluated using an equilibrium distribution function $f^0$ in the absence of radiation, and it is concluded that $tau_{in}$ is much larger than $tau_{q}$, the single-particle relaxation time due to impurity scattering. However, under the irradiation of a microwave capable of producing magnetoresistance oscillation, the distribution function of the high-mobility electron gas deviates remarkably from $f^0$ at low temperatures. Estimating $tau_{in}$ using an approximate nonequilibrium distribution function rather than using $f^0$, one will find the system to be in the opposite limit $1/tau_{in}ll 1/tau_{q}$ even for T=0 K. Therefore, models which depend on the assumption $1/tau_{in}gg 1/tau_{q}$ may not be justifiable.
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