Hollywood is poised to make “historic” improvements in the number of female characters in films within 10 years, the actor Geena Davis has predicted, after decades in which the comparatively low numbers of women and girls onscreen have not risen.

The Oscar-winning actor told the Guardian she was very confident that filmgoers would notice differences in mainstream Hollywood movies within the next few years, in part thanks to work she has done lobbying producers and directors to include increased numbers of less cliched female characters in their films.

Davis, the star of Thelma and Louise, A League of Their Own and The Accidental Tourist, for which she won the best supporting actress Oscar in 1989, founded a research institute into women in the media in 2007, after noticing, while watching children’s TV with her daughter, how few of the characters were female.

Its research found that since 1946, the ratio of female characters in film has not changed “despite all the times when people say, ‘Now there’s been Hunger Games, now there’s been Thelma and Louise, surely now things will change.’ But they don’t,” she said.

“It’s really about unconscious bias, and my theory is that we’re instilling that from the beginning by the entertainments we aim at little children.”

Geena Davis (right) starred with Susan Sarandon in Thelma and Louise. ‘It changed my life,’ says Davis. Photograph: MGM/Everett/Rex Features

Speaking before a symposium at the British Film Institute (BFI) in London on gender in media, at which she gave the keynote address, Davis said she was very optimistic about the future because of the reaction she had received from Hollywood insiders when they were presented with her institute’s research.

“I go directly to talk to the creators, the decision makers, and the response has been overwhelming. Lots of TV and movies have come out now that we know we have impacted, so I feel very confident predicting that the needle will move significantly within the next few years, and it will be historic.

“For seven decades it has not moved significantly, and I believe that it will.”

While conceding that the still low numbers of female directors or producers was “a whole other problem”, Davis said there were simple changes that any filmmaker could make.

“What I recommend as a very easy step is: before you cast something, just go through and do a gender check and change a bunch of first names to female. Voila! You have some very unstereotyped female characters.

Another “very easy fix” would be to specify that crowd scenes are 50% female, she said, since research showed the current proportion was only about 17%.

“Everywhere I go I bring that up, and they say, ‘Why are we doing that? Let’s fix that right away!’ So there are very simple steps that you can take.

“The default is so male in our society that it just doesn’t occur to people to say, ‘Why isn’t the boss or the best friend or the landlord a woman, it so easily could be?’”

Jennifer Lawrence in The Hunger Games, another film that it was hoped would lead to more starring roles for women. Photograph: Murray Close/Publicity image from film company

Davis said she did not yet ask directors to make more female-led movies, “because there’s some, just, holistic resistance to that in Hollywood. I say, ‘Make whatever you were going to make, and just put more women in it. Just cast more women.’”

Addressing the audience at the BFI London film festival, Davis said the reaction from female filmgoers to Thelma and Louise, for which she was Oscar-nominated in 1992, had “changed the course of my life … It cemented my passion for wanting to empower women.”

It was impossible to “snap our fingers” and immediately change the poor representation of women in politics or business, she said, “but there’s one category that could be changed overnight, and that’s onscreen. We can change what our future looks like.”

Pointing out that the rate of progress to date suggested it would take 700 years to achieve gender parity onscreen, Davis said: “I predict that we are going to be able to take both those zeros off that number, and move the needle very soon.”

• This article was amended on 9 October 2015. An earlier version gave the wrong year for Geena Davis’s Oscar nomination for Thelma and Louise.