It is true that the NCVS generally reveals more crime than the UCR.
There are two ways index that measure crimes in the United States: the Uniform Crime Reporting (UCR) and the National Crime Victimization Survey (NCVS). These programs depend on the United States Department of Justice and were designed to measure the impact of crime in the country. The UCR started in 1929 and is operated by the FBI, and measures statistics on murder, aggravated assault, forced robbery, burglary, arson, and car theft. The NCVS is operated by the Bureau of National Statistics and was created in 1973. It measures statistics on r*pe, sexual assault, and home robbery.