Getting good information on domestic violence and sexual assault is challenging. The extent of domestic violence and sexual assault is difficult to measure. The quality of data and the difficulty of measuring violence are barriers. Among the gaps noted in the book, Understanding Violence Against Women,^[1] are:

• Lack of information about the prevalence of violence among marginalized populations, including women of color and low-income, homeless women and children
• Little conceptual understanding of ethnicity, race and other structural factors that may affect the context in which women experience violence
• Inconsistencies across data sets with defining terms such as violence against women, interpersonal violence, rape and sexual assault and intimate partner violence.

Also, sexual assault and domestic violence are hidden and under-reported crimes. The reasons for not reporting vary with the individuals and circumstances. The 1998-2002 National Crime Victimization Survey found that 40% of females did not report incidents of family violence to police.[2] 

Most national and local domestic violence and sexual assault statistics derive from victimization surveys and criminal justice data reporting systems. There are discrepancies between the information produced by each of these methods because the surveys are self-reports while criminal justice data is based on police reports. Where this is the case, a footnote will explain the incongruence. Nevertheless, there are some estimates of domestic violence and sexual assault prevalence rates at the national, state and county levels. Some local data, if it is present, is incomplete and out of date. Therefore, where King County data is unavailable, national and state statistics will be substituted.