This article presents the heterogeneity analysis according to the method developped by Gail (1978). This method was used to assess if mortality data (local/national) are similar among different age groups, this latter being one of the conditions for comparative mortality ratings describe the data with validity. Moreover, this method being comparable to the variance analysis, the population may be split up according to some hypothesis to be tested. We have applied it to the incidence and mortality of stomach cancer in Québec from 1984 to 1988.