The number of women working behind the camera in Hollywood's top-grossing films has changed little over the past decade despite a slight uptick last year, an annual study released on Tuesday has found.

The "Celluloid Ceiling" study from San Diego State University's Centre for the Study of Women in Television and Film said seven per cent of the top 250 films at the U.S. box office in 2014 were directed by a woman, a one percentage point increase from 2013.

"It's not really moving much one way or the other," said study author Martha Lauzen, who added that the number of films directed by women in 2014 has declined to seven per cent from nine per cent since the study began in 1998.

Seventeen per cent of key off-screen figures — which includes directors, writers, producers, executive producers, editors and cinematographers — were women last year, the study found, also a one percentage point rise from 2013 but unchanged from 1998.

Lack of women behind camera an industry-wide problem

"This is clearly an industry-wide problem that requires and industry-wide solution," Lauzen said. "As an industry, film has not taken on this issue of women's chronic underemployment."

The study comes as Hollywood's awards season revs into high gear following Sunday's Golden Globe Awards and the upcoming Academy Awards nominations on Thursday.

Angelina Jolie's "Unbroken" only film by a woman to crack top 100

Ava DuVernay's historical drama Selma is the only early Oscar favourite this year to be directed by a woman, while Angelina Jolie's World War Two biopic Unbroken is the only film by a woman to crack the top 100 at the U.S. box office in 2014.

Only one woman, Kathryn Bigelow in 2010 for The Hurt Locker, has won the best director Oscar in 86 years of Hollywood's top honours.

The study considered 2,822 behind-the-scenes workers and found women were most highly represented as producers at 23 per cent and executive producers at 19 per cent.

Women comprised 18 per cent of editors, 11 per cent of writers while cinematographers were the lowest represented job at five per cent.

Greater emphasis on ethnic diversity as opposed to gender diversity

Lauzen said one issue facing women is a greater emphasis in Hollywood on ethnic diversity as opposed to gender diversity.

"The sex of the director is incredibly important because the research shows that the sex of the director is related to the percentage of female characters that we seen on screen," Lauzen said.

"This is a very complex industry and a very complex problem," Lauzen added. "There isn't a magic bullet here.