[malandrew]

Some companies actually are able to disproportionately hire many of the women available to be hired in the industry.

Company A has a hard time hiring women because Company B had a few more and better female engineers early on. Network effects take over as the company grows affording it the opportunity to hire far more women than other tech companies.

This infographic shows the ratios at a bunch of companies from those with gender ratios below the higher education pipeline ratio to those well above that ratio: http://do-better.studiometric.co/

Women earn 18% of computer science degrees: http://nces.ed.gov/programs/digest/d12/tables/dt12_349.asp

That table shows the ratio at that sample of companies to be around 19% women. Assuming those companies are representative, that is a 1% different in favor of more women than men based on the pipeline feeding the industry.