How exact a science is movie tracking? Lately -- not very.

Over Memorial Day weekend, Warner Bros.' “Sex and the City 2” was forecast to take in around $60 million. It ended up making just $36.8 million.

A week earlier, DreamWorks Animation’s “Shrek Forever After” was on track to take in about $90 million, but it ended up opening to just $70.8 million.

Then last weekend, the opposite happened with Sony's "The Karate Kid." Its domestic opening beat the high end of pre-release forecasts by a stunning $20 million.

What's going on?

These days studio executives are not the only ones to wonder why the opening predictions of research firms -- to which they pay millions of dollars each year -- are so frequently off?

Talk to top executives at one of the major tracking services -- OTX, MarketCast and National Research Group -- and they’re likely to tell you that predicting a film’s opening gross at the domestic box office is really a “parlor trick” and not what their core service is all about.

“The real use of tracking is to measure the effectiveness of the marketing weeks out from release, so you can make adjustments while there’s still time,” said Vinny Bruzzese, president of the worldwide motion picture group for OTX. “By the time the official prediction comes out on the day of the release, it’s fairly useless.”

(See accompanying story: "Tweeting Beats Tracking [4].")

“The purpose of tracking is to provide a snapshot of the marketplace and how (studio marketing) materials are being received,” added an official for another tracking firm, who declined to be named. “The purpose is not to project what the market is going to be.”

Except that's really how studios use the information.

The movie market-research business is more competitive than ever, with yet another new firm, Screen Engine -- started by former OTX research guru Kevin Goetz -- getting off the ground.

While research films for the most part use similar methodologies -- and all employ subtle proprietary differences -- each is trying to stand out as the leading predictive force in a business that often defies accurate forecast.

Like it or not, these research companies are often defined by their ability to accurately predict what films will make their first weekend in the marketplace.

And while most seem to understand that gauging the precise amount of intent-to-see among hundreds of thousands, if not millions, of people remains an imprecise science, studio officials still find themselves surprised when the predictions are off on Sunday morning.

So what gets in the way of the numbers being right?

Well, there’s the well-known cause of the expectations game. Tracking firms are under intense pressure to deliver a number that doesn’t put their client studio in the position of looking like it didn’t meet or exceed the estimate.

“I’d much rather estimate too low than too high,” conceded one tracking-firm official.

Meanwhile, the numbers are often spun by competitive studio forces to be read too high, so that their rival looks like it didn’t have a good opening.

But there are plenty of other factors distorting the numbers.

One studio marketing official surmises that there’s just too much tracking these days -- and too many people with access to tracking who don’t know how to effectively read the data.

Just over a decade ago, the executive noted, the movie business used one tracking firm, NRG, which was headed by Catherine Paura and Joe Ferrell. “They were the only company in town that did it, and it was hard to get tracking,” the studio marketing official explained. “They didn’t even email it to you."

These days, he said, tracking data is ubiquitous, with reports flying all over town every Thursday, and plenty of people unequipped to analyze those reports forming -- and spreading -- too many false conclusions.

More importantly, since Paura and Ferrell were the only game in town, the marketing official added, they weren’t afraid to give the straight dope.

“Catherine would tell you if your opening was going to suck,” he recalled. “Today, there are some of these guys who will try to blow smoke up your ass.”

Since Paura and Ferrell departed NRG in 2003, the business has undergone an interconnected transformation/proliferation.

Two years ago, Kevin Yoder, who worked under Paura and Ferrell at NRG, joined MarketCast, which was founded in 1987 by sociology professor Joseph Helfgot and two academic colleagues. 

Bruzzese, who co-developed MarketCast’s initial movie-tracking systems, left for OTX several years ago to develop a tracking system that was entirely internet-based. He was joined a short time later by Goetz, who had served as a focus-group/test-screening moderator for NRG.

The systems used by the research firms vary. NRG culls information through a “multi-mode” method combining phone, internet and live person-to-person consumer polling.

MarketCast, meanwhile, joined OTX in January in conducting all its movie-related research online, polling a weekly sample of 2,000 frequent moviegoers.

The objectives of all this research, of course, are fundamentally the same: to find out how many people are aware of an upcoming movie and, among those who are aware, to gauge how many intend to buy tickets to the film.

This latter objective becomes challenging under certain circumstances.

For example, a movie like "Sex and the City 2" caters to a core female fanbase, many members of which may have been avid watchers of the HBO series from which the movie was spun off, but not such avid moviegoers. And it's quite difficult to gauge the intent-to-see of a person who doesn't go to the multiplex that often.

Irregular release patterns also complicate things.

Tracking officials based their "SATC2" estimates on the opening of the first installment, which opened on a three-day non-holiday weekend in 2008 to $57 million. But Warner Bros. ended up releasing the sequel several days earlier, on a Thursday, meaning by the time the weekend accounting period arrived, many of the more rabid fans had already seen the film, and they weren't so anxious to see it again so soon.

On the other hand, big tentpoles such as “Iron Man 2” and “Toy Story 3” often present market-awareness indicators of nearly 100 percent. But when the pool of people who know about a specific film gets to be that large, it becomes almost impossible to accurately predict how many people will actually go out and see it.

Certainly, there are no crystal balls.

“All data collection methods are flawed and filled with idiosyncrasies,” noted one tracking-firm official.

A studio marketing official put it less diplomatically: "Today, any f---ing moron with an email account can get tracking. And you get plenty of people who don’t know how to read the data going around telling people that a movie is going to open to $250 million.”