Harkavy, Oscar (1995). «Beginnings of the Modern Population Movement». Curbing Population Growth: An Insider's Perspective on the Population Movement. Col: The Springer Series on Demographic Methods and Population Analysis. New York: Springer. pp. 23, 25. ISBN978-0-306-45050-1. doi:10.1007/978-1-4757-9906-4_2. Cópia arquivada em 16 de março de 2022|arquivourl= requer |url= (ajuda)|acessodata= requer |url= (ajuda)
Harkavy, Oscar (1995). «Beginnings of the Modern Population Movement». Curbing Population Growth: An Insider's Perspective on the Population Movement. Col: The Springer Series on Demographic Methods and Population Analysis. New York: Springer. pp. 23, 25. ISBN978-0-306-45050-1. doi:10.1007/978-1-4757-9906-4_2. Cópia arquivada em 16 de março de 2022|arquivourl= requer |url= (ajuda)|acessodata= requer |url= (ajuda)