"All my black friends have a bunch of white friends. And all my white friends have one black friend."

That's the memorable punchline of a Chris Rock bit from 2009 on interracial friendships. And according to some recent number-crunching by Robert Jones of the Public Religion Research Institute, there's a good deal of truth to that statement.

Let's consider the average white American and the average black American, and let's say, for simplicity's sake, that each of them have 100 friends. If you were to break down their respective friend networks by race, they would look something like this.

If you're interested in how PRRI arrived at these numbers, see the methodological note at the bottom of this post.

In a 100-friend scenario, the average white person has 91 white friends; one each of black, Latino, Asian, mixed race, and other races; and three friends of unknown race. The average black person, on the other hand, has 83 black friends, eight white friends, two Latino friends, zero Asian friends, three mixed race friends, one other race friend and four friends of unknown race.

Going back to Chris Rock's point, the average black person's friend network is eight percent white, but the average white person's network is only one percent black. To put it another way: Blacks have ten times as many black friends as white friends. But white Americans have an astonishing 91 times as many white friends as black friends.

There are a number of factors driving these numbers. Simple population counts are one of them: There are more white people than black people in the United States, so it makes sense that the average American is going to have more white friends than black friends.

Another factor is our tendency to seek out and associate with people who are similar to us in any number of ways - religiously, politically, economically and, yes, racially, too. The polite term for this phenomenon is "sorting," and it affects everything from political polarization to income inequality to the racial differences in friend networks seen above.

As PRRI's Robert Jones writes in the Atlantic, Americans' segregated social circles have influenced responses to the events in Ferguson, Mo., over the past few weeks. Polls show deep divides between blacks and whites on everything from the role of race in Ferguson to the appropriateness of responses by protestors and police.

The numbers above offer insight into why so many whites have expressed bafflement over protesters' responses to the shooting of Michael Brown. The history between many black communities and the police forces that serve them is long, complicated, often violent and characterized by an extreme imbalance of power. But as Robert Jones notes, most whites are not "socially positioned" to understand this history -- simply because they know few people who've experienced it.

To be fair, the numbers suggest there is plenty of racial self-selection in black Americans' friend networks, too. But focusing solely on black-white relations, there's a pretty big difference between having only one member of a given race in your friend network and having eight of them.

In fact, PRRI's data show that a full 75 percent of whites have "entirely white social networks without any minority presence." The same holds true for slightly less than two-thirds of black Americans.

The implication of these findings is that when we talk about race in our personal lives, we are by and large discussing it with people who look like us.

How PRRI calculated the racial breakdowns of friend networks

As part of their American Values Survey, PRRI researchers asked respondents to name up to seven people with whom they regularly discussed important matters. They then asked a battery of demographic questions about these people -- their relationships to their respondents, as well as their gender, religion and, germane for these purposes, their race. They used these numbers to derive average racial breakdowns of the friend networks of the average black, white and Hispanic survey respondent.