Microsoft chief executive Satya Nadella's gaffe over women, pay raises and karma comes as the US tech industry is facing up to questions over diversity and gender equality.

Nadella, named CEO at the tech giant in April, swiftly backtracked from his comments in which he suggested working women should trust karma for pay raises.

"I answered that question completely wrong," Nadella said in a memo to staff, aiming to quell a firestorm over his comments at a conference on Thursday.

Yet Nadella touched a nerve at a time when Silicon Valley faces renewed scrutiny over the gender pay gap, and a lack of diversity in both the workforce and top management.

"The tech sector is still a non-traditional occupation for women," said Ariane Hegewisch, study director at the Washington-based Institute for Women's Policy Research, which monitors issues on women and employment.

"There's not a lot of evidence that karma has been friendly to women in this area."

Research earlier this year by Joint Venture Silicon Valley, a California think tank, found that men in the region who hold graduate or professional degrees earn 73 percent more than women with the same educational qualifications. The gap was 40 percent for those with a bachelor's degree.

An "Equal Pay Project" campaign launched this week calculated that American women over the course of their careers are paid $435,000 less than male counterparts, adding up to a staggering $29 trillion in aggregate.

In recent weeks, major tech firms have been looking at the issue with "diversity reports" that examine the composition of the workforce.

Microsoft reported earlier this month that its staff was only 29 percent women. At Google, the figure was 30 percent. For Facebook, the percentage of women was 31 percent, but just 15 percent in technical jobs.

- The 'geek culture' -

According to research from the National Center for Women and Information Technology, citing census data, women obtained 18 percent of computer science degrees in 2012, down from 37 percent in 1985. The report said women held 25 percent of jobs in the technology industry, down from 37 percent in 1990.

Some blame the male-dominated geek culture.

Researcher Catherine Ashcraft of the University of Colorado said that despite "a wealth of educational efforts to promote girls' participation in computing," there has been little increase in the number of women in the field.

She said these programs often fall short because they "take a narrow view of their purpose, ignoring important factors that shape girls' identities and education/career choices -- not least broader narratives around gender, race, and sexuality."

The tech sector has its share of well-known female CEOs -- Marissa Mayer at Yahoo, Meg Whitman at Hewlett-Packard, and co-CEO Safra Catz at Oracle -- despite the small proportion in the industry overall.

Hegewisch said that the tech sector has become in some ways more difficult for women since the 1980s.

"The geek culture has gotten stronger and the work-all-night culture has gotten stronger, so this might be pushing women out," Hegewisch told AFP.

She said women remain underrepresented in just about every segment of the tech industry, in contrast to some other fields like finance.

"Women might study math or science, but they might go into general business, because the working conditions and culture (in tech) are not that welcoming," she said.

Nadella's comments came coincidentally during an on-stage discussion at the Grace Hopper Celebration of Women in Computing conference in Arizona.

The Microsoft chief stunned the audience by saying that women, instead of asking for a raise should just trust "that the system will actually give you the right raises as you go along."

Nadella later scrambled to damp down the controversy, in comments in Twitter and in a memo to Microsoft staff.

But Hegewisch said that the fact that Nadella made the slip-up at a conference for women in computing suggests he lacks a grip on the issues.

"It shows he doesn't really have a clue about the debate," she said. "And it shows just how far we have to go."

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