But in the current business climate, it's even harder to make projections based on a stock formula, even though that formula is an integral part of deciding which projects get greenlit and at what budget level.

Most studios calculate probable sales using the movie's theatrical box office as a guide. But the maturing market for DVDs and recession-weary consumers are forcing studios to rethink these established equations.

Distribs are scrambling to understand why "Taken" and "Gran Torino" were big DVD titles while "Paul� Blart: Mall Cop," which posted similar box office, has moved off shelves more slowly. The best they can figure so far is that the first two titles can be considered part of the more reliable action genre while "Paul Blart" is a trickier-to-predict comedy offering.

Execs lately are walking into the planning process with lower expectations, based on DVD sales declines this year. At the halfway mark in 2009, DVD and Blu-ray sales combined are down 13.5% vs. the year before, according to the Digital Entertainment Group. And combined DVD/Blu-ray sales in 2008 had already fallen 12.7% from 2004's $16.6 billion, considered the industry's peak, according to Adams Media Research.

One studio's typical projection is that DVD titles generate 85¢ for every $1 that a movie grosses at the box office. But since 2008, that return has slipped roughly 18% to 70¢ per $1 of box office.

"There are more variables than you had in the past, where it's not who guesses the best but who is looking at the tea leaves best; there are definitely clues," says one studio chief.

In the past, studios could also gauge a title's prospects based on how similarly themed DVDs moved off shelves previously. But with sales dropping so steeply of late, studios are forced to pluck comparison titles from the 2008 pool only, and they pray their parallels hold up.

Beyond the B.O. and barometers of similarity, studios are adding and subtracting points depending on genre and recognizability. For example:

Plus: action DVDs with perceived strong packaging and a favorable street date

Minus: films in the over-saturated horror genre

Plus: installments within existing franchises

Minus: anything in the notoriously inconsistent areas of drama, comedy and romance

"Certain film genres, such as action, are performing better than ever this year," says Lionsgate chief operating officer Steve Beeks. "But there has never been a simple formula. Genre, cast, artwork and release date are a few of the myriad factors that go into our projections. And now ... we have to layer in a whole new dimension."

Sony Pictures Home Entertainment had the right combination of factors, and scored a true DVD hit with "Underworld: Rise of the Lycans." The third iteration in the vampire-vs.-werewolves action series, in fact, would have been a big seller in any year, not just by 2009's lowered standards.

"Despite the declines in the market over the last three years, our most recent film came very close to duplicating the performance of our last entry in the franchise (2006's "Underworld: Evolution)," Sony prexy David Bishop says. "Titles with very large built-in awareness, whether it be from a franchise or from another property, have had a tendency to be among the year's best performers on homevideo."

But even the most carefully thought-out formula isn't foolproof. There are just too many contributing factors to weigh into the equation.

"Is it better to be in one genre or another? I don't know," says another studio exec of his prediction process. "Action films do perform better than most, but then they cost more to make. Warner has a pretty good track record with Harry Potter."

The exec, however, cautions that Warners might have to downsize its expectations for "Harry Potter and the Half Blood Prince," given the recession. "But as a known entity, it might have an easier time than 'Hangover.' I've seen forecasts for the same movie that are 40% different from each other."

One studio recently wrapped up an exhaustive but ultimately maddening study meant to find parallels between successful movie franchises like Harry Potter, Lord of the Rings, Shrek, and the Matrix series. The analysis focused on whether timing between installments impacts sales. No consistency was found from one franchise to the next.

Each had been brought to market so differently than the rest, the only pattern found was that there was no pattern.

Despite the head-scratching, studios still rely on forecasts of DVD sales. The essential guideline right now is to avoid overestimating potential. In fact, the only formula in this changing market is that there really is no formula.

"Data is used up to a point, and you'll get to a point where the data is creating unacceptable results," says a homevid honcho. "People are going to try to rationalize a different forecast. And you can find different data points to rationalize different forecasts."