MODELING THE VARIANCE OF DISPERSION MEASURES OF RADIO PULSARS

On the basis of a highly simplified model for small scale structure in the electron density distribution in the Galaxy, we argue that the sp read of expectation values for the dispersion measure at given distanc e is proportional to the square root of the dispersion measure as foun d from a smooth model for the electron distribution. We show that this simple method leads to appreciable improvement in the description of dispersion measures in a full population synthesis.