Reported data of metastable zone width (MSZW) and induction time for solutions seeded from outside were analyzed with a new unified mathematical model. In the model, the points the MSZW and the induction time are attained are both treated as a point that the number density of seed-originated crystals or newly-formed crystals from seed crystals by secondary nucleation mechanisms reached a fixed (but unknown) value, and secondary nucleation is assumed to occur in steady state. The effect of cooling rate on the MSZW and the relation between the induction time and the supercooling were explained in a unified manner. The MSZW and the induction time were related with each other and once either the MSZW or the induction time is determined, the other can be estimated for the same material system for a given experimental set-up. (C) 2009 Elsevier B.V. All rights reserved.