 A popular theory is that the rape of Jewish women in captivity brought about the law of Jewish identity being inherited through the maternal line, although scholars challenge this theory citing the Talmudic establishment of the law from the pre-exile period.Since the anti-religious "Haskalah" movement of the late 18th and 19th centuries, "halakhic" interpretations of Jewish identity have been challenged.The total number of Jews worldwide is difficult to assess because the definition of "who is a Jew" is problematic; not all Jews identify themselves as Jewish, and some who identify as Jewish are not considered so by other Jews.