APA
United Nations. Department of International Economic and Social Affairs, . (1991). World population prospects, 1990. New York: United Nations.
Chicago
United Nations. Department of International Economic and Social Affairs, . 1991. World population prospects, 1990. New York: United Nations.
Harvard
United Nations. Department of International Economic and Social Affairs, . (1991). World population prospects, 1990. New York: United Nations.
MLA
United Nations. Department of International Economic and Social Affairs, . World population prospects, 1990. New York: United Nations. 1991.