Dive summary:

• The return on investment for Facebook and Twitter can be derived from a formula invented by HubSpot.
• Churn rate is key to determining the value of Facebook likes or Twitter followers. 
• This formula brings social media to the hard metrics of dollars and centers of ROI math. 

From the article:

… I've noticed a disturbing trend over the past few years in the social media end of the communications world. Much of the advice and strategy I hear boils down to little more than "unicorns and rainbows" superstitions like "engage in the conversation" and "be awesome." …