The kinetic theories on the polymerization rate and polydispersity for the persistent radical-mediated living radical polymerization were quantitatively tested by experiments for the bulk polymerization of styrene with PS-DEPN with or without BPO at 80 degreesC, where PS is polystyrene, DEPN is N-tertbutyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, and BPO is benzoyl peroxide. For the BPO-free system, experiments agreed with the theories on an absolute scale, showing a 2/3-order time dependence of conversion index and a 3/8k(d)-dependent time evolution of polydispersity index, where k(d) is the dissociation rate constant. It was also experimentally demonstrated for the first time that the conventional initiation can not only increase the conversion but also lower the polydispersity at a given polymerization time t (at least when t is small), as was predicted by the theories.