Sarah Watson is the deputy director of a non-profit research group in New York: the Citizens Housing and Planning Council. For the last five years, the organization has been studying new concepts in housing. Watson says the number of people living by themselves in the United States has increased dramatically — In the 40s and 50s it was less than 10%. Today, that population is closer to 30%. …people are getting married later, getting divorced at higher rates than they once did and are living longer.  And Watson says the supply of housing for single people hasn’t kept up with this changing demographic.