"About one-quarter of Jews alive today (25 percent) have left the country in which they were born and now live somewhere else. By contrast, just 5 percent of Christians, 4 percent or Muslims and less than 3 percent of members of other religious groups have migrated across international borders."From a Pew survey discussed here. A propos of not much, I remember listening to an academic's discussion of census data on ethnic categories a few years back, in which the speaker told us that Japanese-Americans and Jews have the highest rate of out-marriage; Chinese the least. American blacks, so it was said, marry out less in this generation than before.