The number of serious violent crimes not reported to police fell from 50 percent to 42 percent from 1994 to 2010, says a study by the Bureau of Justice Statistics.

Highlights from the report include: 

• Rape and sexual assault continue to be unlikely to be reported to police at a startling rate - 65 percent went unreported between 2006 and 2010, the study found. Household thefts (67 percent) are also unlikely to be reported, while motor vehicle theft is the most likely (17 percent unreported). 
• About 3 in 10 (31 percent) of victimizations involving a weapon and an injury to the victim went unreported between 2006 and 2010. 
• Victims give a variety of reasons for not reporting a crime to police - most commonly because they found another way to deal with the incident that didn't require police attention.

But the study indicates confidence in police has become an increasing issue - in 1994, 21 percent of victims did not report because they didn't think the crime was important enough to warrant police attention, while 10 percent believed the police could not or would not help. In 2010, 15 percent did not think the crime was important enough to report, versus 20 percent who felt police could not or would not help.

Within that data set, the percentage of people who said they did not report because they didn't think police would find the crime was important enough to address rose from 5 percent to 12 percent between 2005 and 2010.

More than 20 percent of unreported violent victimizations against people living in urban areas were not reported because the victim believed police would not or could not help, the report says.. However, overall, victims in suburban areas (54 percent unreported) and those making more than $50,000 a year (56 percent) were less likely to report a crime to police than those in urban areas (51 percent) and those making less than $25,000 (50 percent).