Ranking is by points accumulation, and the rules is as follow:
1. your friend posts on your wall --> 3 points
2. you mention your friend on your wall --> 3 points
3. your friend comments your post on your wall --> 2 points
4. your friend likes your post on your wall --> 1 point
The statistics is according to the latest 200 posts on your wall,
however, due to length limitation, the data from FB is usually less than 200.
Besides, the size of name is based on individual points compared to the highest points.
In other words, the greater the gap of points, the greater the difference of sizes of names.