The electric field correlation function of light scattered from a polydispersed population of spherical particles having log-normal distribution with varying polydispersity is simulated. The correlation function with different polydispersity is compared with the method of cumulants over a wide range of correlation time. The large positive deviation of the method of cumulants at long correlation time is identified. This necessitates the truncation of the data at long correlation time or use of an appropriate weighting function to eliminate errors in the analysis. A modified cumulant analysis is used to overcome the limitation of truncating the correlation function. QELS data from polydisperse samples of micelles, liposomes and polyaniline nanoparticles are compared using the two methods. This method can be extended to the analysis of other multi-exponential decays such as stress relaxation, positron annihilation and NMR relaxation. (c) 2006 Elsevier Inc. All rights reserved.