Abstract
The probability density function for the value of b in the formula logn(M)=a-bM estimated by the author's method has been obtained in an exact form. This function leads to a simple method to test the statistical significance of the difference between two b-values. Application of this method to SUYEHIRO'S data on foreshocks and aftershocks of the great Chilean earthquake of 1960 indicates a significant difference in b-value between the foreshocks and the aftershocks at the 98% confidence level.
