James Brasuell wrote:

The Finnish government has a population register that collects data about where individuals live. The researchers got access to this data and were able to follow individuals as they moved from place to place in the Helsinki metro area. This data allowed them to trace exactly how the construction of new luxury apartment buildings in high-end neighborhoods impacted the broader housing market.

Regarding the findings, the research finds that the process of filtering can start with high-end development in wealthier neighborhoods and end with cost savings in low-income neighborhoods.

Here is how Lee defines and describes filtering:

When a new apartment comes on the market, it starts a chain reaction. Often, the person who rents the new apartment is moving out of an old apartment in the same metropolitan area. That creates a vacancy that can be filled by another renter. That person, in turn, may be vacating a third apartment. These “moving chains” can extend for six or more steps, with Helsinki residents playing a game of musical chairs to find better or cheaper housing options.