Gentrification is a particularly tricky subject for anyone interested in understanding how and why cities change, and who benefits from that change. In part this is because it’s emotionally laden—it deals with fundamental issues of home, community, and belonging, not to mention longstanding and painful race and class divides within our cities. In part it’s also because it’s hard to agree on a baseline understanding of the facts. Even the definition of the term “gentrification” is up for debate, both within academic circles and in common understandings.

If we want to clearly understand what’s going on in our neighborhoods, we need to make a point of separating and being more precise about concepts that, while related, aren’t the same thing. Gentrification (which refers to how a place is changing) and displacement (which is something that happens to individual people or communities in that place) are two such concepts that often get used in the same breath or even as synonyms, but shouldn’t.

A new study from New York City using health care data to track the moves of individual low-income families helps us disentangle gentrification and displacement from each other, and make some sense of this seemingly contradictory reality:

poor people are often displaced from gentrifying neighborhoods, yet

gentrification does not appear to (usually) cause displacement.

Kriston Capps has written an excellent summary of the study over at CityLab. From that summary:

The new study, conducted by researchers at New York University and released by the National Bureau of Economic Research, used Medicaid records to track the paths of children living in New York City from January 2009 to December 2015. This extraordinarily useful trove of data allowed researchers to see where families lived and moved, even month-to-month. By following the changing addresses of a large cohort of low-income children over the course of this seven-year period—a time of rapid gentrification for neighborhoods like Crown Heights—the researchers were able to show where these children started, and where they ended up.

This kind of study is the holy grail for anyone looking into neighborhood change, because it follows individuals over time. A lot of the confusion around these issues stems from the fact that most available data (for example, from the U.S. Census Bureau) provides an overall snapshot of a neighborhood’s demographics at a point in time, but does not track how individual people or households come and go. So, for example, if 100 low-income families move out of an area, and 100 different families, but with similar incomes, education levels, race, etc. move in, census data will make it look like this neighborhood isn’t changing at all. In fact, as our friends at City Observatory (among others) have observed, change is a constant in most urban neighborhoods: things are in flux more than is obvious from observing either the physical place or data about totals and averages.

So what did the NYU researchers find? Capps delivers the key take-away:

They found that the majority of low-income children born into neighborhoods that later gentrified stayed in those neighborhoods, a finding that contradicts the most upsetting (and prevailing) theories about gentrification: Namely, that the original residents of a neighborhood, especially the most vulnerable ones, are forced out when more affluent residents arrive.

Hooray! The pernicious evil of low-income residents being uprooted from their neighborhoods was a myth all along and we can all stop fretting about it! Right?

Well, not exactly:

To be sure, these families live incredibly transient lives: Children in low-income households were very likely to move more than once over this period, regardless of their neighborhood, residence, or demographic group. But low-income children living in neighborhoods that experienced gentrification were not more likely to be displaced than those living in persistently low-income neighborhoods that did not gentrify. “These kids move a lot, whether their neighborhood gentrifies or it doesn’t gentrify,” [study co-author] Glied says. “A very large fraction of these kids move in the first several years of their lives. It turns out, that fraction is not correlated with whether the neighborhood that they’re born into gentrifies. Poor kids are not very residentially stable.”

The rest of the study delivers a range of complex and sometimes seemingly contradictory findings. For example, those who moved out of gentrifying neighborhoods—versus persistently poor ones—tended to move longer distances and were more likely to leave New York City altogether. But they tended to move to safer neighborhoods. Those who stayed tended to see a reduction in poverty—but also ended up attending worse schools.