Hollywood studios are squeezing more into their weekend box office reports this year, adding ticket sales from Thursday shows and making big movie openings look even more lucrative.

In 2013, 14 films with opening-weekend sales of more than $50 million were screened on Thursday nights in U.S. and Canadian theaters, according to data from Fandango.com, the ticket-buying service. That compares with two last year, when most early showings started at 12:01 a.m. Friday.

The Thursday shows give studios extra business on a slow night and, in some cases, the chance to trumpet record totals with the extra day tossed into the traditional Friday-to-Sunday tally. While the new accounting method suggests a better reception for a movie, it can muddle comparisons with earlier films.

"It really destroys the concept of, How did the movie do?" said Peter Sealey, a former chief marketing officer for Columbia Pictures.

A recent example is "The Hunger Games: Catching Fire." While Lions Gate Entertainment Corp. officially released the film Friday, Nov. 22, theaters across the U.S. began showings at 8 p.m. the day before.

Lions Gate reported that "Catching Fire" generated $158.1 million in opening weekend sales — $5.6 million more than the first "Hunger Games" movie, released in March 2012. The new film’s total was bolstered by $25.3 million in Thursday night screenings — including midnight shows — complicating comparisons with the first "Hunger Games," which didn’t play earlier than midnight.

"We’re entering a new period where you can put an asterisk by opening weekends and say it includes Thursday, too," said Phil Contrino, an analyst with researcher Boxoffice.com.

The earlier screenings grew more common after a July 2012 shooting at a midnight showing of Warner Bros.’ "The Dark Knight Rises" in Aurora, Colo., left 12 dead, and traffic at late-night shows dropped off. The policy at Fox is to start Thursday shows at 10 p.m. or later and include them in the weekend totals, said Chris Aronson, executive vice president for distribution at the 21st Century Fox Inc. unit.

"For us, 10 p.m. became the new midnight," Aronson said.

In 2013, virtually every studio added Thursday showtimes for many of their biggest films while also running midnight shows.

Ultimately the quality of the film will decide whether it takes in a lot of money, not early screenings, Aronson said.

Representatives of Lions Gate and other major studios would not comment, as did the Motion Picture Association of America trade association.

Research outfits have gone along, sometimes footnoting that Thursday receipts are included.

"We do the numbers as reported by the studios," said Paul Der­gara­be­dian, senior media analyst with Rentrak Corp. "We don’t break out the raw data."

The change has muddied all-time rankings. "Iron Man 3," from Walt Disney Co., had the third-biggest opening of all time, with a $185.4 million haul, according to Box Office Mojo, which ranks films in dozens of categories. That put the film ahead of "Dark Knight Rises," from rival Warner Bros., which didn’t have Thursday screenings.

"Does it stretch the box office a little bit? Yes," said James Marsh, an analyst with Piper Jaffray & Co. who recommends buying Lions Gate stock and is neutral on Burbank, Calif.-based Disney. "It’s nice to have a headline, some kind of record opening."

Boxoffice.com will include Thursday in Friday-to-Sunday totals as long as the studios do, according to Contrino. Representatives from BoxOffice Mojo, owned by Amazon.com Inc., didn’t respond to requests for comment.

By starting the weekend early, the studios gain benefits that go beyond bragging rights.

Positive comments from Thursday-night moviegoers on Twitter and Facebook help fill seats from Friday to Sunday, said Jeff Bock, an analyst with researcher Exhibitor Relations Co. Kids at school on Friday can tell their friends they’ve already seen a widely anticipated film, he said.

Movie chains, which split ticket revenue with the studios, say they’re happy to fill seats in the middle of the week.

"How they account for it, it’s not something we’re concerned with," said Bud Mayo, chairman and chief executive officer of Digital Cinema Destinations Corp., an exhibitor based in Westfield, N.J. "If I were Lions Gate I’d be doing it, too."