  Albert-Laszlo Barabasi introduced a model which exhibits the bursty nature of
the arrival times of events in systems determined by decisions of some humans.
In Barabasi's model tasks are selected to execution according to some rules
which depends on the priorities of the tasks. In this paper we generalize the
selection rule of the A.-L. Barabasi priority queuing model. We show that the
bursty nature of human behavior can be explained by a model where tasks are
selected proportional to their priorities. In addition, we extend some of
Vazquez's heuristic arguments to analytic proofs.
