Why do rates of sexual assault prevalence vary from report to report?

"All crime data have flaws, but sexual assault data are notoriously inaccurate. Why are these data so problematic? And what are the consequences for how we address sexual violence in the United States? Data on rape and sexual assault suffer from inconsistent estimates and underreporting, leading to misunderstandings about the extent of the problem and adequate policy solutions. Let’s look at two major sources of information on the topic: survey-based studies that estimate prevalence of sexual assaults and criminal justice system data. In this post, we look at data on female victims of sexual violence, since most existing reports and statistics focus on women. Data on sexual assault against men are especially sparse; we know even less about the experiences of male victims" (p. 1). Sections cover: two different surveys, two different stories-National Crime Victimization Survey (NCVS) and the National Intimate Partner Sexual Violence Survey (NISVS); and why criminal justice data can be misleading.