Arizona auto insurers have raised rates overall since the start of 2008 after cutting overall rates in 2007, data from the state Department of Insurance show.

In 2008, insurers raised rates a market-weighted 3.72 percent, the agency reported. So far this year, insurers have filed rate changes averaging an increase of 3.8 percent, on an unweighted basis, according to a Star analysis of state data.

Reasons for rate increases vary by company but are mainly a reflection of each company's loss experience and rising costs, said Ron Williams, executive director of the Arizona Insurance Council, a nonprofit industry group.

He noted that in 2006, the state's 20 largest auto insurers cut rates by about 5 percent.

The biggest insurers cut rates by a similar amount in 2007. Overall in 2007, insurers cut overall auto insurance rates by about a third of one percent on a market-weighted basis, says the state Insurance Department. (Click on chart below.)

One factor in recent increases may be losses insurers are taking on investments they make to help meet their reserve requirements, Williams said.

In Arizona, insurers can change rates without prior approval, but regulators can challenge rates they believe are "inadequate or unfairly discriminatory."

The state offers auto insurance premium surveys and other tools on its Web site, www.id.state.az.us