Received: 26 September 2017
Accepted: 5 January 2018
First Online: 23 January 2018
: I am the Inaugural Hoffman Professor of Family Sociology and Demography, Distinguished Senior Scholar of the Department of Sociology, and Affiliate of the Population Research Institute at Pennsylvania State University, University Park. I received a PhD in Demography from the University of California, Berkeley in 1972.
: The author declares that he has no competing interests.
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