That was just a web page. The research was published in a journal Demography, by 3 researchers from the University of Pennsylvania: http://link.springer.com/ar

That was just a web page. The research was published in a journal Demography, by 3 researchers from the University of Pennsylvania: http://link.springer.com/article/10.1007/s13524-012-0157-1 http://link.springer.com/article/10.1007/s13524-012-0157-1