This week Google revealed that more than four fifths of its tech workforce in America are men – a situation it described as “miles from where it wants to be”.

Yet the gender balance within Google broadly reflects that within the wider IT workforce in the US.

Since 2005 women have consistently occupied just over one quarter of software developers, network administrators, and other computer-oriented roles in the US. During that period, however, the proportion of women carrying out these jobs has fallen very slightly from 27 percent to just over 26 percent, according to figures from the US Bureau of Labor Statistics (BLS) Current Population Survey (CPS).

The small proportion of female workers in IT-focused roles isn’t a reflection of the make-up of the “professional” workforce as a whole, according to the BLS CPS, which showed women accounting for 43 percent of “professional and related” occupations in 2013.

The decreasing share of women in the US IT workforce is mirrored by a decline in the number of women getting Bachelor’s degrees in Computer Sciences and Information Sciences: between 2005 and 2011, numbers of female graduates in those disciplines fell by 9.3 percent to just over 43,000.

The number of women receiving Bachelor’s degrees in these subjects began rising from 2009. But due to a larger increase in the number of male students graduating in the subject the proportion of women receiving the qualifications dropped to its lowest point in almost 40 years in 2011. That year, women accounted for 17.6 percent of graduates.

The question of why so few women pursue an IT-related career relative to other professions has been tackled by many academic studies.

An analysis of these studies by the American Association of University Women suggests that girls are put off pursuing careers in subjects linked to maths and science early in their education.

“Unfortunately, the ancient and erroneous belief that boys are better equipped to tackle scientific and mathematical problems persists in many circles today, despite the tremendous progress that girls have made in science and math in recent decades,” the report says.

“Research shows that negative stereotypes about girls’ suitability for mathematical and scientific work are harmful in measurable ways. Even a subtle reference to gender stereotypes has been shown to adversely affect girls’ math test performance. Stereotypes also influence girls’ self-assessments in math, which influence their interest in pursuing science, technology, engineering, and mathematics careers.”

Although there are findings of boys outscoring girls in tasks requiring spatial skills, (Linn & Petersen, 1985; Voyer et al., 1995), which the AWWU says may “may deter girls from pursuing math or science courses or careers”, the AWWU analysis points out these skills can be improved through education.

Women that do pursue a career in a science or technology-related field may go on to encounter various forms of bias, research has found. For example a 2007 study Why are women penalized for success at male tasks? The implied communality deficit by Heilman and Okimoto found women may be disliked for being competent in what were perceived to be traditionally male work roles. The AWWU report suggests this may explain why women working in STEM (Science, Technology, Engineering and Mathematics) roles leave at higher rates than their male peers.

There is also anecdotal evidence of sexist behaviour within the tech industry, which may or may not reflect wider practices, but which is unlikely to attract women to enter the industry. Recent reports range from the presentation of an app called Titstare at a TechCrunch Disrupt event last year to the recent #1reasonwhy hashag on Twitter detailing female games developers’ experience of discrimination.

Various initiatives have started up in recent years aimed at encouraging more girls and women to learn about computing, such as Ada Developers Academy and Black Girls Code. For its part, Google says it has given more than $40 million to organizations working to bring computer science education to women and girls.

But Google wants to employ more women, and Laszlo Bock, senior VP of people operations at Google, hopes that transparency on its gender balance will be “a really important part of the solution”.