Movie ticket prices continued to inch up at the end of 2013 -- all as attendance and box-office revenues slipped for the year. During the last three months of 2013, there was a nearly 4% hike in the average ticket price, according to the National Association of Theatre Owners. Much of this rise resulted from the ticket price increases of high-profile 3D and IMAX films.Movies like the heavy Oscar-nominated space drama “Gravity” helped to stoke the 3D category. Other big 3D theatrical sellers include Walt Disney's musical "Frozen" and Peter Jackson's "The Hobbit: The Desolation of Smaug." For the full 2013 year, the average ticket prices grew just over 2% to $8.13, from 2012.According to the Motion Picture Association of America, total box-office revenues were down 4% in 2013 to $10.36 billion from $10.83 billion in 2012. In addition, there were 7% fewer tickets sold in 2013 -- 1.27 billion -- versus 1.36 billion in 2012.The top-grossing U.S. distributed movie was Walt Disney’s “Iron Man 3,” which pulled in $408.9 million in box office revenues.