<i>We've ranked the current Y Combinator Summer 2013 batch by Mattermark Score – which awards points to each company on a weekly basis for increasing their website traffic, mobile downloads, inbound links, Twitter followers, Facebook likes, and LinkedIn followers.</i><p>It's hard for me to understand how this formula could be a valuable measure of growth of a startup, since most of these things can be easily purchased. I'd guess that growth of Facebook Likes, Twitter followers, LinkedIn followers and website traffic are more accurately a measure of a company's ad spend than their actual growth in revenue and users.