A model of relaxors as superparaelectrics with a distribution of the local transition temperature has been investigated. The necessary model parameters are obtained from the analysis of the static polarization response of lead magnesium niobate and then employed in simulations of the frequency-dependent dielectric properties. The present model is compared with a previously published model of relaxors, based on a single transition temperature but with a distribution of the size of the polar regions. Both of them describe some characteristic features of relaxors, i.e. the shift of the peaks in temperature dependence of the real and imaginary parts of the dielectric permittivity with frequency and the broadening of the relaxation time spectrum on cooling. However, a model which takes into account the distribution of the size of the polar regions describes qualitatively correctly the shape of the relaxation time spectrum.