In the study of religions in Russia, the "ethnic principle" is based on the assumption that the entire number of people belonging to a given ethnic group are adherents of that group's traditional religion. This principle is often used to estimate the magnitude of very small groups, for instance Finnish Lutheranism at 63,000, assuming that all the 34,000 Finns and 28,000 Estonians of Russia are believers in their historical religion; or German Lutheranism at 400,000, assuming that all Germans in Russia believe in their historical religion. However, whether for small or larger groups, this approach may lead to gross mistakes.