But, honestly, as I said in another comment, I'm not sure how much these numbers mean. With respect to to the MA negative numbers, if you've been anywhere near the Boston/Cambridge area recently the idea that there's this mass net exodus of people is pretty silly. Certainly if you've looked at Boston Metro real estate prices or the construction going on in the Seaport or around Kendall Square.
EDIT: It may also be related to MA people living in NH for tax reasons.
Well not necessarily "mass" (pun intended?) but -2% from 2000 to 2015. Note that everyone who moved from other cities in Massachusetts to Boston (and Boston burbs) are considered neutral by this metric. And there's always bound to be graduates of those Boston universities headed for the other coast. Also note that things are very different in Boston and elsewhere in 2016 from how they were in 2000.
I suspect that may have something to do with it. Maybe Vermont has more initially out-of-state college students, or they represent a higher relative proportion? Also, keep in mind that NH is 2x the population of VT and is close to a major metro area (Boston, ~1hr away). I have friends that live in Southern NH and commute to northern regions of Boston for work.
I'd like to see a 20-year later study that looks into the number of people that went to VT for school (from out of state), went to another state for a career (not a huge number of options in VT) and returned late. Everyone I know that went to school there wants to do this; they love the place but couldn't find a non-service/tourism job post-graduation.