Gentrification and displacement have become so intimately linked in how we talk about certain neighborhoods that they've begun to fuse together, the one word silently implying the other, "displacement" giving "gentrification" its sinister tone (and, presumably, the premise for questions like this one).

Decades of research on revitalizing neighborhoods, however, have left a messy and conflicting record on this front.

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It's certainly inaccurate to suggest that all moves out of a changing neighborhood should be counted as "displacement." And part of the difficulty here also lies in the blurry line between what people choose to do, and what's forced on them. If a family chooses to sell its home to profit off rising property values, is it displaced? What about a family that can still afford the rent but leaves because the bar scene has become too rowdy?

Large datasets rarely reflect these nuances. And researchers are often trying to understand a group that by definition isn't around to tell us why they moved, or whether they felt pushed out. Measuring displacement, Rowland Atkinson wrote in 2000, is like trying to measure the invisible. The people we want to know about have scattered from the place we're trying to understand.

A final complication: Neighborhood change takes place at an incredibly slow pace (despite how it sometimes feels when new restaurants are sprouting on, say, Washington's 14th Street). That means a study that runs from 1970-1977, or even 1989-2002, doesn't capture at lot of what's going on. And because the pace of change is gradual, the Fed paper points out, it's hard to contrast a "before" and "after" picture of a single neighborhood. There's no bright line separating the two.