Silicon Valley 2016 Diversity Report.
https://apps.revealnews.org/silicon-valley-diversity-list/
Reveal from The Center for Investigative Reporting surveyed 211 of the largest Silicon Valley tech companies that were required to submit EEO-1 diversity reports to the federal government for 2016.
Twitter's report is more or less what you would suspecte, but there are some other interesting insights.
https://www.documentcloud.org/documents/4107437-Twitter-2016.html