In 2009, the Academy decided to change their voting rules for Best Picture. They did this to be able to include more than five contenders after The Dark Knight was shut out in 2008. While preferential balloting has always been used to find the nominees in most categories, only in 2009 did the preferential ballot come into play to pick the winner of Best Picture.
But there was another change that impacts the nominees. In 2009 and 2010, Academy members were asked to pick ten and not five Best Picture contenders. That gave them a lot more freedom in what they might choose, from big movies to small movies, foreign films to domestic, critically acclaimed or popular. But members complained that they didn’t want to be bothered with ten, that they far preferred choosing only five. In 2011, the Academy changed their rule again so that Academy members would choose only five. They would pick the winners the same way, with a complicated voting procedure that essentially means a film needs a good number of number one votes to get in, but they would extend the cut-off so that if there were films that came close to making it in could still get in. So far, we’ve had two years with nine nominees. I expect this year, with so many great films in the race, to also have nine. Apparently it’s mathematically difficult to get ten. Preferential balloting rewards films that are passionately loved, even if they are also passionately hated.