There are a number of official statistics concerning the population of the Jewish Race and the Religion. But I have never seen one which tried to account for the definition used on this site. A definition which never expires, and does not concern itself with personal practices, knowledge, or the purity of the genetics. For thousands of years, particularly during the birth of Christianity, Jews have left their faith and their communities, most of them certainly forgetting their heritage after a generation or two. Has their ever been any work done to estimate the number of lost Jews, and calculate a probably number of descendants (on the mothers side)?
In short, going by the biblical definition of who is a Jew, what would be a good estimated population number?