The main reason for the dramatic relationship with age is that younger voters are more inclined to register as independents than older voters are. As the chart shows, while the proportion of Democratic-independent and Republican-independent pairs shrinks from the youngest couples to the oldest couples, the proportion of Democratic-Republican pairs actually doubles — i.e., the purple band becomes bigger.
I guess it all depends on what they are “other” about…
Of course, there are many ways to interpret this data, and they all don’t point to Democrats being more close-minded than are their Republican and Independent peers.
One could easily imagine that this trend among Democrats was significantly impacted by the reality of Donald Trump becoming President, and the fact that communities in defeat often turn inward.
We also evaluate the degree of sorting through another exercise: Suppose that all of us choose partners from the pool of people who share our age and geographic location.
So, a 30-year-old New Yorker seeks a spouse from the pool of other 30-year-old New Yorkers.