Matthew Coller and Pro Football Focus analyst Kevin Cole talk about his "Improvement Index" which is meant to quantify how much a team has improved during the offseason. The Vikings are presently on the positive side of the chart but many NFC teams are on the negative side. Why are the Rams lower and the Lions last on the list? How much does the Vikings' lack of answers at safety, offensive line and edge rusher matter? Is Washington the most improved team?