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

[Josh]

I had just sent requests to people I know. They accepted and when they first appeared on my chat, they were on the top of the list even when they were online (usually it shows online people and then offline people in the list.)

One girl I just sent a request to is now appearing on my box of 9 friends. I have only seen her profile about 3-5 times only. This girl is appearing as six on my box of 9 friends.

I had added another girl at the same time and I have also seen this girls profile only once and she is appearing on the box of six friends. This girl is appearing eighth on my box of 9 friends.

Just wondering why/how Facebook chooses the friends to put on the box of 9 friends even when I have seen their page only a minimal amount. Could it be they are looking at my Facebook profile, I haven't chatted, liked or commented on any of their statuses only looked at their profile. (I have seen other people profiles a lot and they haven't appeared on the box of 9 friends.

[pri✍]

I wonder why so many people in here Y!A do wasting time thinking over nitty gritty like this. It's just random, as why on earth FB will spend their time on this things while there are many other things to be corrected & done that is much more important?