This is especially interesting:
"People marry along a line of integration 38% more often than chance. For example, 7-1 and 3-6 marriages were common, as were male 2s-female 4s, male 3s-female 9s, and several other such combinations."
I have wondered about this before. It seems it would be better for one person than another though.
Example - integration lines go from 6 to 9 to 3 to 6 again. Disintegration lines go from 6 to 3 to 9 to six again. Integration goes towards healthy. Disintegration goes towards unhealthy.
So, a 6 with a 9, could help drive the 6 to be more "healthy" as their partner falls directly into their line of integration. I have wondered if it is bad for the 9 though because the 6 is in the direction of their line of disintegration which goes more towards the unhealthy side. Could it be that a 3 is better for a 9 than a 6? Then would the 9 would not be as good for the 3?
Edit: For those who don't know what I'm taking about with lines of integration/disintegration, look here:
http://www.enneagraminstitute.com/intro.asp