Your driving record seems a legitimate risk for insurers to consider when they price auto insurance. But your marital status?

Yes, young men in red sports cars will pay more for coverage than everyone else, but it’s hard to see how being a widow, or being divorced or separated, has much to do with the odds you’ll be in an accident.

Yet single, separated, and divorced people, and widows, often pay more for policies than married customers, according to a new study from the Consumer Federation of America(CFA). In the study, when a husband died, the cost of state-mandated liability coverage for the widow rose by an average of 20 percent at four of six major insurers, the study found.

The consumer advocacy association collected quotes for state-mandated minimum liability insurance from the websites of six insurers—State Farm, Farmers Insurance, Nationwide Mutual Insurance, Liberty Mutual Insurance, Geico, and Progressive—in 10 cities ranging from Baltimore to Portland, Ore. Among the six, only State Farm didn't charge different rates based on marital status, the report found.

Why should marital status factor into pricing? Good question, says the CFA, which wants state regulators to take a harder look at whether it's fair to use marital status and certain other factors. The CFA's executive director, Stephen Brobeck, noted in a press release that single, separated, and divorced people tend to have lower incomes than married people and that therefore using marital status in pricing "tends to discriminate against low- and moderate-income Americans." 

Marital status is a legitimate factor in judging a person's risk, says Loretta Worters, vice president of communications for the Insurance Information Institute, a non-profit group supported by the insurance industry. Actuarial studies show that someone who is married is less likely to be in an accident than someone who is single, she says: "It's not 'I'm not married and am being charged more.' There's a bigger picture that has to do with your driving habits and how they affect you. It's about the accidents."

Typically, when people get married, they become more responsible and more concerned about their health, Worters says, and their increased risk aversion shows in a driving record that includes fewer accidents and tickets.

The CFA said that pricing differences between single and married couples persisted regardless of age and that a 2004 National Institutes of Health study that the industry likes to cite is flawed. That study shows single people having higher driving injury rates than married people, but the CFA says that it "was based on data collected in New Zealand around 1990 involving only 138 injuries, a substantial minority of which involved driving motorcycles. And the difference in injury rates was only about one percentage point." 

The CFA study found that four of the six major insurers didn't charge higher prices for domestic partners than for married couples, but that both Geico and Progressive often did in certain cities, citing Baltimore, Tampa, Louisville, Minneapolis, Denver, and Phoenix. Progressive also charged more in Houston, the study said. 

Marital status is just one of many elements that can work their way into auto insurance pricing, and that the CFA has studied over the years. In 2013, it released a study about the impact of credit scores on auto insurance rates, saying that the use of credit scores by insurers discriminated against lower-income drivers. It has also released a study looking at the connection between auto insurance rates and education.