<ref>Tom W. Smith, "Adult Sexual Behavior in 1989: Number of Partners, Frequency of Intercourse and Risk of AIDS," ''Family Planning Perspectives'', Vol. 23, No. 3, May/June 1991, p. 104. </ref> | <ref>Tom W. Smith, "Adult Sexual Behavior in 1989: Number of Partners, Frequency of Intercourse and Risk of AIDS," ''Family Planning Perspectives'', Vol. 23, No. 3, May/June 1991, p. 104. </ref> |