As previously stated, standard deviation tells us less than we’d like about data which do not fit into a bell curve. Average deviation tells us more. The specific observations about 1790 from before still hold, but looked at through a better lens, the regions don’t have quite the same ambiguity.
By national standards, in 1790 the normal enslaved population of a place should come between 4.65% and 30.86%, still a large range but not so huge as the standard deviation gave. Most of the North falls below that by a healthy margin, but New Jersey and New York exceed it. They fall into the lower extremity of the normal range.
But that’s by national standards. A normal Northern place has an enslaved rate between 0.06% and 4.02%. By that standard, New Jersey and New York don’t belong. Nor, of course, do the places with no slaves at all: the future Maine, Massachusetts, and Vermont. Those three locals have too much freedom, if by a small margin, to fit with the more typical Northern slavery of Connecticut, New Hampshire, Pennsylvania, and Rhode Island. One could call them the North within the North and New Jersey and New York the South within the North.
Down South, nowhere has a notably low rate of slavery. On the far side of the national range, Georgia, Maryland, South Carolina, and Virginia stand out. All four have significantly greater numbers of their people enslaved. But the South doesn’t amount to a home away from home for New Jersey and New York. The region’s normal range runs from 23.15% to 43.86%. South Carolina beats that top band by a narrow margin, keeping its place of distinction as the most enslaved of the most enslaved. But Delaware, Kentucky, and Tennessee all under perform by the region’s norms. They don’t quite belong in the South any more than New Jersey and New York belong in the North, demographically speaking.