Popenoe, Paul; Disney, Dorothy Cameron (1960). Can This Marriage Be Saved? (First ed.). New York: The Macmillan Company. Library of Congress number: 60-8124.
books.google.com
Gosney, E.S.; Popenoe, Paul (1929). "Chapter 7: Voluntary Sterilization". Sterilization for Human Betterment: A Summary of Results of 6,000 Operations in California, 1909-1929. New York, New York, US: The Macmillan Company. p. 59. ISBN9780140511918. "Troublesome Delinquents" section{{cite book}}: ISBN / Date incompatibility (help)
gutenberg.org
Popenoe, P.; Johnson, R H (1918). "Chapter XIV: The Color Line". Applied Eugenics. New York, New York, US: The Macmillan Company.
