For companies whose workforce includes more than 100 engineers, the proportion of women on engineering teams falls far below the national average of 25 percent, according to data from Pinterest engineer Tracy Chou. But when it comes to startups with up to seven engineers, the prospect for women vastly improves. At those companies, they comprise at least 50 percent of the engineering team.

What Gives?

Some of the big companies with a smaller proportion of women engineers may surprise you: They’re not all old, mature Fortune 500 businesses. Some are relatively new players like Etsy, Dropbox and Pinterest. And it's not a case of their not trying hard enough. For example, Etsy counts women as many of its customers and has put money behind its effort to recruit female engineers. The company offers grants for living expenses to women who attend its free Hacker School, which ramped up participation from seven women in the spring of 2012 to 61 in that summer of 2012. So why does the proportion of women drop as the engineering team grows? One possibility is networking, which is a key way for companies to identify candidates. If male engineers recommend their friends and former associates in tech -- which is largely male -- it maintains the cycle of hiring a greater percentage of male engineers.

Small Companies, Bigger Opportunities

Out of the 93 companies on Chou's list, nine have engineering teams with a 50 percent of greater proportion of women. As noted, these teams are small, with the largest having a staff of seven. What's the common theme among these businesses? In all but one case, their founders are women. At Scientific Learning, where four women are on its seven-person engineering team, Paula Tallal is one of four co-founders. Levo League has two women co-founders, Caroline Ghosn and Amanda Pouchot. Its six-person team has four women on-board. One exception to this women-founder idea is the Hackbright Academy, which has two male co-founders. However, the academy is designed specifically to increase the number of female software developers. Of the three engineers on staff, two are women. In other words, the academy walks the walk.