Your Annual Reminder to Ignore the U.S. News & World Report College Rankings - John Tierney - The Atlantic
Another one
I remember discussing this with someone at the graduate office and he mentioned some other factors
1. Research papers published: it doesn't take into account how many papers are in progress. So if one university has 1 paper published, the university gets a better score than the others not publishing any papers. And this doesn't take into account the quality of the publishing. So one school can also gets high credits if several of its professors publish papers at the same year.
2. Buildings: if you get a new building, you'll get rewarded in the ranking.
There are some things that are quite subjective and overall, it's OK to see the top 10, but after that it becomes fuzzy. It also will depend on the program. US News lumps everything into one.