The presence of strong chain length selectivity behavior during initialization in the RAFT process is an experimental observation. The mechanistic underpinning of the observation is,however open to interpretation. The rates and concentration profiles for the cyanoisopropyl-dithiobenzoate-mediated polymerization of styrene at 70 degrees C can be relatively well reproduced by either the slow fragmentation or intermediate radical termination models. the use of modeling that provides a fit to the data is an important tool, but should be considered as additional evidence in support of experimental data rather than as experimental evidence in and of itself.