Only 11 percent of all engineers in the U.S. are women, according to Department of Labor. The situation is a bit better among computer programmers, but not much. Women account for only 26 percent of all American coders.

There are any number of reason for this, but we may have overlooked one. According to a paper recently published in Journal of Personality and Social Psychology, there could be a subtle gender bias in the way companies word job listings in such fields as engineering and programming. Although the Civil Rights Act effectively bans companies from explicitly requesting workers of a particular gender, the language in these listings may discourage many women from applying.

The paper – which details a series of five studies conducted by researchers at the University of Waterloo and Duke University – found that job listings for positions in engineering and other male-dominated professions used more masculine words, such as "leader," "competitive" and "dominant." Listings for jobs in female-dominated professions – such as office administration and human resources – did not include such words.

A listing that seeks someone who can "analyze markets to determine appropriate selling prices," the paper says, may attract more men than a list that seeks someone who can "understand markets to establish appropriate selling prices." The difference may seem small, but according to the paper, it could be enough to tilt the balance. The paper found that the mere presence of "masculine words" in job listings made women less interested in applying – even if they thought they were qualified for the position.

Shanley Kane, a software product manager in the Bay Area, says these subtleties should not be overlooked. "It's worth paying special attention to how the 'masculine-themed' words they tested for – competitive, dominate, leader – denote power inequalities," she explains. "A leader has followers. A superior has an inferior."

The paper sheds new light on a big issue for technology companies. At a talk at First Round Capital's CTO Summit last year, Etsy CTO Kellan Elliott-McCrea called for more gender diversity in the tech world – and not just for altruistic reasons. Diverse teams are better problem solvers, according to a study conducted by Kellogg School of Management, and enabling cross-departmental communication is easier when engineering teams are more diverse, Elliott-McCrea said.

To be sure, job listings aren't the only thing keeping women out of engineering and computer science. Part of the reason for an imbalance has historically been the lack of women being trained in the first place. But a shortage of women in non-life-science degree programs only accounts for part of workplace disparity. For example, 38 percent of geoscience Ph.D graduates are women, but only 26 percent of assistant professors are women, according to research cited in the Waterloo paper.

Women may also be more likely to leave male-dominated fields. According to research published by the Harvard Business Review, 52 percent of women in science, engineering and technology end up leaving the field, never to return.

Subtle forms of institutional bias may play a role in pushing women out of these fields, and that includes the job listings like those examined in the Waterloo paper.

In the first two Waterloo studies, researchers gathered random samplings of job listings and split them into two groups: male dominated professions and female dominated professions. They threw out listings from neutral professions, or professions such as management in which the gender proportions were unknown. Using previously published lists of gendered words, the researchers analyzed the listings and found that while male dominated fields tended to use more masculine words in job listings, female dominated fields didn't use more feminine words.

In other words, job listings in female dominated professions were more neutral.

The other three studies used a set of fake job listings for male-dominated professions (engineers, plumbers), female-dominated professions (registered nurses, administrative assistants), and neutral professions (real estate agent, real estate sales manager). For each profession, the researchers created both a "masculine" job listing and a "feminine" job listing.

In one of these studies, researchers found that participants were more likely to guess that there were more men at the companies with masculine-worded listings and more women at feminine-worded listings, regardless of the the profession. In other words, a nursing ad that included a high number of masculine words made the participants think that there were more men at the company that created the listing, and a computer programming listing with feminine words made the participants believe more women worked for the company. Participants in the study were asked what made them think a company had more men or more women, and not one of them mentioned wording of the listing.

Another study used this set of fake listings and asked participants to rank the job's appeal and their perceived level of "belongingness." Women ranked feminine-worded listings higher in both appeal and belongingness. Men ranked feminine-worded listings slightly lower in appeal and just as high in belongingness.

The last study was similar, but it also asked participants to rate their ability to perform the job in question. Wording did not affect women's perception of their ability to perform the job, only their perception of the job's appeal and their level of belongingness.

The implications are obvious, especially as the number of women graduating with degrees in science, engineering, and technology increases. For example, the graduating computer science class of Harvard University was 41 percent percent female in 2012, Elliott-McCrea told audiences at the CTO summit. "An inability to hire talented females will start to significantly impact your ability to recruit altogether," he said.

Kane says workplaces that use the language of power inequality send a message that women aren't welcome. The researchers seem to agree, concluding that the language of the listings emerges from a systemic bias against women, as evidenced by the fact that the language of job listings for female-dominated professions weren't similarly biased in favor of women.

The Waterloo paper cites several more documented barriers to women's advancement in male-dominated professions, including "exclusion from informal networking opportunities necessary for advancement," "unwelcome or patronizing work environments," "double standards for promotion and hiring," and "underperformance due to stereotype threat."

Kane says that fixing the language of job listings won't fix the problem if the culture doesn't change as well. "I hope that mass market education on the ways sexism manifests itself doesn't mask the disease with symptoms," she says.