“In terms of box office, the law of diminishing returns does not apply to `Harry Potter.’ It seems to be getting better with age,” said Paul Dergarabedian, Media By Numbers president, who noted that the July 21 publication of the seventh and final “Harry Potter” novel likely helped drive interest in the latest film.

“It has the effect of creating even more excitement for both properties,” Dergarabedian said. “It’s a synergistic match made in heaven to have the book and movie come out within a couple weeks of each other.”