How does Facebook determine the box of 9 friends on Facebook timeline?

[Josh]

Is it to with how many profile views.

1st Friend: I've seen this friends page a lot. I haven't liked anything, commented on anything, or IM chat this person.
2nd Friend: Used to view this friends profile a lot. Now not at all yet still on the box of 9 friends and second.
3rd Friend: This friends randomly sent a IM chat one day, ever since then, this friend has been third on the box of 9 friends. I haven't seen this persons profile, liked any statuses, or commented on anything of this persons.
4th Friend: Never view this persons profile page (Never communicated on Facebook)
5th Friend: On rare occasions this friend sends me IM chats. I have never seen this friends profile.
6th Friend: Just added this person on Facebook. Only seen this friends profile 3-5 times in total. Not viewed the friends page the whole of today.
7th Friend: Never view this persons profile page. (Never communicated on Facebook)
8th Friend: Just added this person on Facebook. Only viewed this persons profile once.
9th Friend: I have never communicated with this person on Facebook.

What determines the box of 9 friends on Facebook timeline? Is it the number of times the friend has viewed your page.