In recent years, the number of dead malls increased significantly in the early 21st century because the economic health of malls across the United States has been in decline, as identified by high vacancy rates. From 2006 to 2010, the percentage of malls that are considered to be "dying" by real estate experts (have a vacancy rate of at least 40%), unhealthy (20–40%), or in trouble (10–20%) all increased greatly, and these high vacancy rates only partially decreased from 2010 to 2014. In 2014, nearly 3% of all malls in the United States were considered to be "dying" (40% or higher vacancy rates) and nearly one-fifth of all malls had vacancy rates considered "troubling" (10% or higher). Some real estate experts say the "fundamental problem" is a glut of malls in many parts of the country creating a market that is "extremely over-retailed".