http://www.rainn.org/statistics confirms the claims made by the Author of the Article in question and has additonal information for those interested in statistics on rape and sexual assualt survivors.

Rain's data was collected from the following scources:

National Institute of Justice & Centers for Disease Control & Prevention. Prevalence, Incidence and Consequences of Violence Against Women Survey. 1998.
U.S. Department of Justice. 2003 National Crime Victimization Survey. 2003.
U.S. Department of Justice. 2004 National Crime Victimization Survey. 2004.
1998 Commonwealth Fund Survey of the Health of Adolescent Girls. 1998.
U.S. Department of Health & Human Services, Administration for Children and Families. 1995 Child Maltreatment Survey. 1995.
U.S. Bureau of Justice Statistics. 2000 Sexual Assault of Young Children as Reported to Law Enforcement. 2000.
World Health Organization. 2002.
U.S. Department of Justice. 2005 National Crime Victimization Survey. 2005.