Another indicator that Jews tend to be clannish

I showed recently that Americans overwhelming select someone of the same race for a best friend.  Friendship is a good measure of how well groups are mixing, or, on the other hand, how much they cluster.

In this post, let's focus on religion. Does your best friend share your religious affiliation?  I used General Social Survey (GSS) data to answer this question (sample size = 1,932).  Here are the percentages who indicated a religious match between themselves and their best friend:

Percent whose best friend belongs to the same religion

Jews  75.6
Protestants  74.5
Catholics   59.4
None  42.3

Jews emerge as the group that clusters the most.  You might respond that Protestants have basically the same number, but we would expect a high number for a such a large group.  According to the latest GSS, 48.9% of Americans are Protestant, 23.3% are None, 21.2% are Catholic, and 1.7% are Jewish. If Protestants picked their friends at random, their best friend would also be Protestant around half the time. For Jews, a random process would give a Jewish best friend less than 2 percent of the time, and yet the number is over 75%.  This shows an intense level of clustering among Jews.