  The relaxation time approximation (RTA) is a well known method of describing
the time evolution of a statistical ensemble by linking distributions of the
variables of interest at different stages of their temporal evolution. We show
that if all the distributions occurring in the RTA have the same functional
form of a quasi-power Tsallis distribution the time evolution of which depends
on the time evolution of its control parameter, nonextensivity $q(t)$, then it
is more convenient to consider only the time evolution of this control
parameter.
