AdExchanger chats with Rob Norman, GroupM's Chief Digital Officer, who opens up on a number of issues including his views on open exchanges vs. private deals in 2016. "We're going to see less demand for bad supply in 2016. I suspect the amount of inventory that we ever bought in the pure open exchanges was relatively low in comparison to the total impressions in the markets. I'd like to think that [GroupM client] AT&T was buying a lot less than that than the University of Phoenix. The private marketplace is clearly a safe and relevant haven for many significant advertisers. The idea that you can control your supply chain yet still deliver into that supply chain is a happy combination."