Population density data of several systems with and without additives were collected in our laboratory using an MSMPR crystallizer. Two methods for searching crystallization kinetics were used to analyze these data. Crystal growth rate and nucleation rate of zero-size nuclei and effective growth rate and nucleation rate obtained by the two methods are compared. The agreement between the results is generally good for effective rates with the specified crystal size larger than 50 pm, but is violated for smaller crystal size, especially for zero-size nuclei. Thus 50 pm is a good choice for the effective size. The kinetic parameter of the rate equations are also compared. Again, parameters of effective rate equations are more consistent than those of nuclei rate equations. For impure systems the consistency between the two methods is generally poor.