From the NBA official release:
O.J. Mayo’s second place finish is my only strong objection to the tally. Mayo finished behind Eric Gordon in PER, Value Added, Estimated Wins Added, True Shooting Percentage, Assist Rate, Turover Rate. Mayo had the edge in Rebounding Rate, points per minute, usage, and hype.
Like many awards, the criteria for Rookie of the Year is nebulous. Is the question, “Which rookie had the statistically best year?” Or “Which member of the rookie class would you most like to build a team around?” Or “Who was the best rookie on a relevant team?”
Ultimately, the award is meaningless, more so than the others because history will bear out which member of the 2008 Draft Class will emerge as the best pro.