Thanks for checking it out! Haha that's a good question. We grabbed a master list of the world's most valuable startups, based on WSJ's Billion Dollar Startup Club, as well as posts on Fred Wilson's and William Mougayar's blogs (listed at bottom of this post).

Then we realized we had a list of 300+ companies, some private, some public, some acquired, scattered across the world, founded anywhere between 1999 to 2013. Kinda all over the place.

So we decided to filter it down for now to give it some focus: i) founded after 2006, ii) founded in the USA, and iii) private. The list quickly shrunk to 86.

Deciding to keep it to the USA was tough, but we noticed many high-profile startups abroad don't exactly use Twitter very actively, so including them might skew the #'s.

Here's our current list: https://docs.google.com/spreadsheets/d/1ue2UAoKaGf32rGewLXWe...

Sources: http://graphics.wsj.com/billion-dollar-club http://avc.com/2013/11/the-billion-dollar-valuation-club/ http://startupmanagement.org/2014/04/20/the-global-unicorns-...