At Facebook, code written by female engineers was rejected 35 percent more than their male colleagues, according to the findings of a longtime Facebook employee who relayed that data to The Wall Street Journal. For some women engineers, data confirmed their suspicions of gender bias at the social networking company.

The employee who conducted study was described as having been at Facebook several years. She performed her analysis "so that we can have an insight into how the review process impacts people in various groups," according to screenshots of her internal post obtained by The Wall Street Journal. Her identity remains unknown.

Other key points found that women waited 3.9 percent longer to have their work accepted and that their code got 8.2 percent more comments and questions. The researcher analyzed five years of data pulled from the company's open repository of code-review information. This data included an engineer's gender, city, and tenure at the company.

While she started her research last year, gender bias has long been a topic of debate at Facebook and other Silicon Valley tech giants. When the results were brought up at a Q&A with Mark Zuckerberg, he said gender bias was "an issue." Facebook officials conducted their own review of the engineer's study and attributed any gap in rejection rates to the employee's rank. A Facebook spokesperson told The Wall Street Journal that the engineer's analysis was "incomplete and inaccurate."