A couple days back we had an article about Natalie making a new Forbes list, however we didn’t have the actual Forbes article. Luckily, Huc was able to find it. So now we have a proper explanation about how it all works (after the jump) as well as some more specifics about Natalie’s appearance on the list…

Thanks to her work in the new Star Wars movies, Portman has appeared in some of the highest-earning films of all time. But she ranks on our list because of movies like The Other Boleyn Girl, which earned $78 million at the worldwide box office. Like many of the actresses on our list, Portman appears in her fair share of art films, like 2007’s little-seen Paris J’Taime. For every $1 Portman was paid, her films earned an average of $28.

In order to create our list, we looked at the 100 biggest stars in Hollywood. To qualify, each actress had to have starred in at least three movies in the past five years that opened in more than 500 theaters. (In Watts’ case we didn’t count her 2008 film Funny Games because it only played on 288 screens.)

We didn’t include animated films because the actresses aren’t really the draw, and they tend to take pay cuts for voice work.

For past lists we have required that actresses earn at least $5 million per movie, but we decided to waive that this time around. We calculated each star’s estimated earnings on each film (including upfront pay and any earnings from the film’s box office receipts, DVD and TV sales). We then looked at each movie’s estimated budget (not including marketing costs, which are susceptible to accounting chicanery) and box office, DVD and television earnings to figure out an operating income for each film.

We added up each star’s compensation on her last three films and the operating income on those films and divided total operating income by the star’s total compensation to come up with each return on investment number.

Only the last three films? That’s a bit narrow.