BOISE, Idaho (AP) — A new state analysis shows just 4 percent of reported rapes in Idaho result in a guilty conviction of a sex crime.

According to a recently released Idaho State Police report, rape charges are the most likely to be amended or modified to a lesser offense compared to other sex crime charges.

"Sexual violence is a prevalent concern in Idaho with a significant fiscal impact. Results indicate that reports of sexual violence take almost ten times longer to investigate, and are nearly half as likely to result in arrest, charges being filed, and a guilty conviction," wrote Danielle Swerin, senior research analyst for ISP, in her June report.

The report studied crime data between 2009 and 2015 using court and crime incidents collected by the state. Researchers only analyzed reported cases of sexual violence — an important caveat they point out because an estimated 67 percent of rapes and sexual assaults nationwide are not reported to the police.

The report found that overall rate of reported sex crimes in Idaho has been steadily decreasing since 2009 and that the majority of sex crimes are committed by someone known by the victim. The data showed that victims are usually female and under the age of 18. Comparatively, victims of violent crimes — such as robbery, aggravated assault and kidnapping — tend to be older than 18.

Out of the 8,452 sex crimes reported between 2009 and 2015, 3,269 of those were reported rapes. Police made arrests out of 20 percent of those rape charges. Eventually, that number dwindled to 8 percent cases concluding with a guilty conviction with 130 seeing a guilty conviction for an actual sex crime.

"There's definitely room here for more research why that number is so low," Swerin said, adding that her research team did not look into why the disparities took place.

The report also found that 24 percent of reported sex offenses statewide resulted in an arrest between 2009 and 2015. Meanwhile, nearly 50 percent of violent crimes lead to an arrest. That disparity only widened in rural Idaho, Nez Perce, Caribou, Minidoka and Teton counties.

For example, Idaho County saw 17 percent of its 36 reported sex crimes result in an arrest, while 74 percent of its 743 violent crimes ended with an arrest. Over in Nez Perce County, 12 percent of the 269 sex crimes reported saw arrests, while 69 percent of the 3,228 violent crimes saw arrests.