After millions of Americans lost their homes to foreclosure, bargain-hunting investors have stepped in to buy them up.

At first, many investors looked to flip the properties quickly with only minimal repairs or improvements.

Over time, as it became harder to find buyers, the investors began renting the homes en mass to the growing number of people in need of rental housing—including those who lost their homes to foreclosure.

A new study by Dan Immergluck, a professor at Georgia Institute of Technology, is one of the first on-the ground reports about the effect investors are having in rental markets.