NEW YORK (CNN/Money) - It may be the 21st century, but women in the United States still have a long way to go when it comes to achieving economic equality with men, a report issued Tuesday found.

The great divide, however, is not quite as great in some states as in others, according to "The Status of Women in the States," a study published by the Institute for Women's Policy Research, a D.C.-based nonprofit organization whose research for the report was funded in large part by the Ford Foundation.

In order to compare women's employment and earnings opportunities across states, the IWPR took a composite measure by looking in each state at women's median earnings, the difference in men's and women's pay (a.k.a., the wage gap), the percentage of women in the labor force and the percentage of working women in managerial and professional occupations.

Generally speaking, women have fared better in those states with white-collar economies and strong ties to higher education.

To talk about the "best" states for women economically is to talk in relative terms. That's thanks in large part to the wage gap. On average in every state, women earn less than men. Just how much less is a question each state answers differently.

The good news is the wage gap has narrowed in all but four states, in some cases significantly. The smallest gap currently is in the District of Columbia, where women earn 89.2 cents for every dollar men earn for full-time, year-round work. That's well above the national average of 72.7 cents. But women in Wyoming, the worst state in terms of the wage gap, earn only 64.4 cents.

The bad news is "at the rate of progress achieved over the past 10 years, women will not achieve wage parity for more than 60 years," IWPR noted in the study, the fourth of its kind published since 1996.

Some may see the wage gap primarily as a function of women's choices -- for instance, to stay home and raise children, to take less demanding, lower-paying jobs, or to forgo higher education. But that oversimplifies the issue, said Dr. Heidi Hartmann, IWPR's president and CEO.

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"[Women's choices] are based on how they perceive current restrictions," she said, explaining that if women had access to paid family leave, better subsidized child care and wages more on par with those of men -- and if there were a more equal assessment of men's and women's abilities -- women might make different career choices.

In addition there are other things states can do to improve women's chances for economic equality. Stronger enforcement of equal opportunity laws, implementation of pay-equity policies in the public and private sectors and higher minimum wages are among IWPR's policy recommendations.

The IWPR study also looked at women's participation in the labor force and, more specifically, in professional and managerial occupations.

Between 1965 and 2000, the percentage of U.S. women who work has grown from 39 percent to 60 percent, and currently women make up 46.5 percent of all workers (full- and part-time), with mothers constituting the fastest growing group in the labor market, the report found.

Minnesota has the highest percentage of working women, with 70.3 percent on the job in 2000; while in West Virginia, which ranked last, only 51.3 percent of women work.

Women's participation in managerial and professional jobs also has been growing since 1994, but IWPR cites studies showing female managers are unlikely to earn top-dollar in such positions. The District of Columbia ranks No. 1 in the survey, with 48 percent of its working women occupying professional and managerial jobs, compared with a national average of 32.2 percent. Idaho is ranked last among the states, with female managers and professionals making up only 26.1 percent of all women employed in the state.

Taking into account all the factors in IWPR's Employment and Earnings Index, the District of Columbia, Maryland, Alaska, Minnesota and Colorado were ranked highest. The states that ranked lowest were West Virginia, Louisiana, Mississippi, Wyoming and Arkansas.

In another snapshot of women's economic status, the IWPR also took a composite measure of what it defines as a woman's social and economic autonomy in a state by looking at the percentage of women living above the poverty line, the percentage of women with four or more years of college, the percentage of businesses owned by women and the percentage of women with health insurance.

Taking top honors on that scale were the District of Columbia, Maryland, Colorado, Connecticut and Massachusetts. The worst-ranked states were Arkansas, Louisiana, Mississippi, West Virginia and Kentucky.

In addition to economic factors, IWPR's study looks at women's political participation in states, their reproductive rights and their health status to assess which states were "best overall" for women.

Only eight states made the grade according to IWPR's criteria. Massachusetts, Minnesota and Vermont tied for first; Connecticut and Washington tied for fourth; Alaska took sixth place; and Maine and New Hampshire tied for seventh.

The five worst states for women overall were Mississippi, Tennessee, Kentucky, Oklahoma and Arkansas.

(More on the study's findings can be found at IWPR's Web site.)