HONOLULU -- A disproportionate number of Native Hawaiians are making up a segment of the prison population, according to a new study released by the Office of Hawaiian Affairs.

The study looked at eight years of state prison data and drew some startling conclusions. The study took three years and cost more than $300,000. What it found is a growing problem for Native Hawaiians.

"One of the things that became clear in this study was that Hawaiians are developing long-term relationships with the criminal justice system and it has this downward spiral effect. It's kind of like a vortex they get caught up in," said Jim Spencer, professor of urban planning at the University of Hawaii at Manoa.

One of the findings in the study showed Native Hawaiians are serving longer prison and probation sentences than other ethnic groups. On average, a person of Japanese ancestry is sentenced to 14 fewer days of probation than a Native Hawaiian person and Caucasians are sentenced to nearly 21 fewer days.

The study showed that Native Hawaiians make up 24 percent of the general population in the state, but among the incarcerated, that figure jumps to 39 percent. What the study does not show is why.

"What you see from this report is that we need more open conversation and figure out the mechanisms by which this disproportionate representation happens, and that's something we don't know right now; the mechanisms by which it happens," said Spencer.

Researchers said they also want to figure it out how to solve this problem.

"I don't think we're ready to say we need to enforce certain types of legislation. I think what's necessary is for a much more open conversation that we have a problem," said Spencer.

Since 1997, the number of people incarcerated in Hawaii has increased more than 900 percent from 398 people to more then 4,300 people sentenced to more than one year in 2008, the study said.