In Nebraska, rates rose by as much as 108 percent. These increases occurred despite substantial gains in automobile safety and the arrival of several new players in the insurance markets.

Only in California, where a 1988 ballot initiative “transformed oversight of the industry and curtailed some of its most anti-consumer practices,” did insurance prices fall during the period, the CFA report found.

The report said CFA found that the amount that drivers spend on auto insurance in California declined by 3 tenths of one percent, resulting in billions of dollars of annual savings.

The industry has challenged the report's findings.

The Insurance Information Institute said in a reaction that factors other than Proposition 103 played a role in lowering rates. I.I.I. said that a competitive market, less litigation and safer vehicles have made auto insurance coverage in California, and elsewhere, more affordable for drivers.

“The Insurance Information Institute calculated last year that annual auto insurance expenditures for the typical U.S. driver rose only 4.2 percent between 2002 and 2012, even as the Consumer Price Index (CPI) over these same 10 years grew by 27.6 percent,” Robert Hartwig, president of the I.I.I., said.

Indeed, Robert Detlefsen, vice president of public policy for the National Association of Mutual Insurance Companies, charged that the report reinforces CFA's “well-deserved reputation for manipulating statistics and omitting critical information to reach pre-fabricated conclusions.”

Detlefsen cited several examples which he said demonstrated why the report's data and analysis cannot be considered reliable, noting that the CFA report claims that “the average expenditure on auto insurance” country-wide increased by 43.3 percent between 1989 and 2010.

“CFA doesn't say whether this percentage increase is adjusted for inflation, nor does it indicate whether the 'average expenditures' mentioned throughout the report are per policy, per capita or per household,” Detlefsen said.

Detlefsen added that the price of the average vehicle rose considerably between 1989 and 2010, as did the number of cars owned per household and even per capita. As the total insured value of automobiles increased, he said “it stands to reason that the amount spent on auto insurance would increase as well.”

He also said the report fails to consider the most important determinant of auto-insurance prices: claim costs. “Consequently, the reader has no way of assessing the extent to which the increases in the amount spent on auto insurance in any given state can be attributed to increases in insurers' claim costs in that state,” Detlefsen said.

Robert Passmore, senior director of personal lines policy for the Property Casualty Insurers Association of America (PCI), said, “Opponents of competition-based rating systems such as the Consumer Federation of America have the misguided impression that prior-approval systems keep insurance rates down. However, National Association of Insurance Commissioners (NAIC) data demonstrates that on average states with competitive-based regulatory systems have the lowest average annual premiums when compared to the countrywide average and states with prior-approval systems.”

The data, he said, shows preliminary average annual premiums (2010) as: competitive-based states (including Flex-Rating), $901.15; prior-approval states $921.62; all countrywide $907.38.

Passmore adds, “Although the CFA highlights California and Proposition 103, this type of regulatory approach is not a recipe for success. In reality insurers have been able to function despite the stringent, bureaucratic prior-approval rate regulation system. California's competitive auto insurance market is actually the result of a series of tort reform ballot initiatives and court decisions coupled with improvements in highway safety and auto manufacturing as well as California drivers' continued high use of seat belts which lowered the cost of providing insurance, therefore lowering insurance premiums.”

CFA, in its report, said that on the 25th anniversary of Proposition 103, it had found that the proposition delivered over $102 billion in savings for California's motorists, an average annual savings of $345 per household, or $8,625 per family over the entire period.

CFA's Hunter said that that this was the result of strong regulatory oversight and a more competitive market fostered by the 1988 insurance-reform measure.

In the report, CFA looked at each state and evaluated the various types of insurance-regulatory regimes found across the country. Using this data, CFA identified best practices from a consumer-protection perspective.

CFA said that, on insurance costs, it found that the states with the highest average expenditure on auto insurance are Nebraska, Louisiana, Montana, Wyoming and Kentucky; and the states with the lowest increases are Hawaii, New Hampshire, New Jersey, Massachusetts, and Pennsylvania.

As to regulation, the CFA report found that the prior-approval system of regulation, in which insurers must apply for rate changes before they can be imposed in the market, is most effective at keeping rates low; markets that are less or not regulated tend to have the most substantial increases; that the prior-approval 25-year increase was 48 percent, the File and Use system was 60 percent, the Use and File system was 62 percent, the FLEX system was 67 percent and the deregulated system was 70 percent.

“While mildly and strongly regulated states tend to have very or somewhat competitive markets for auto insurance, deregulated and flexible-rating states have the least competitive markets,” the report found.