A number of New York City's most luxurious homes are actually pieds-à-terre or investment properties. In the NY Times article "Why the Doorman Is Lonely: New York City’s Emptiest Co-ops and Condos," Julie Satow examines these empty buildings and how they came to be. She cites Social Explorer's Andrew Beveridge when she parses the data and more about the wealth gap's role.

…The I.B.O. data doesn’t include townhouses or 421a buildings, so there are a lot of misses, but of the condos and co-ops that are captured, the number of nonprimary residents is high,” said Andrew A. Beveridge, the president of Social Explorer, a firm that tracks census data and demographic information, and the chairman of the sociology department at Queens College…

…As for the data that has been uncovered, “it reflects the increasing level of income inequality in the city, that you can buy a relatively expensive condo and not have to occupy it all the time,” Mr. Beveridge said. “Housing has a strange spending curve. If you are poor, you spend a high proportion of your money on housing. Then as you get up into the middle class, people pay off their mortgages and you don’t see as much spending on housing. Then as you get really wealthy, the rich spend a lot on housing, but they do it by having a lot of homes.

Read the full article here.