Democrats are going all in on the War on Women campaign theme once again, focused this time not on free contraception but on the claim that women make only 77% percent of what men make for comparable work.

It is the centerpiece of the 2014 electoral campaign.

Glenn Kessler, WaPo’s fact checker, noted that Obama’s State of the Union claim was not accurate:

“I ask this Congress to declare that women should earn a living equal to their efforts, and finally pass the Paycheck Fairness Act this year.”

There is clearly a wage gap, but differences in the life choices of men and women — such as women tending to leave the workforce when they have children — make it difficult to make simple comparisons.The administration’s back-up document for this statement asserted that “on average women generally make 23 cents on the dollar less than men.” But the White House is using a figure (annual wages, from the Census Bureau) that makes the disparity appear the greatest. The Bureau of Labor Statistics, for instance, shows that the gap is 19 cents when looking at weekly wages. The gap is even smaller when you look at hourly wages — it is 14 cents — but then not every wage earner is paid on an hourly basis, so that statistic excludes salaried workers.

In other words, since women in general work fewer hours than men in a year, the statistics used by the White House may be less reliable for examining the key focus of the legislation — wage discrimination. Weekly wages is more of an apples-to-apples comparison, but it does not include as many income categories.

Economists at the Federal Reserve Bank of St. Louis surveyed economic literature and concluded that “research suggests that the actual gender wage gap (when female workers are compared with male workers who have similar characteristics) is much lower than the raw wage gap.” They cited one survey, prepared for the Labor Department, which concluded that when such differences are accounted for, much of the hourly wage gap dwindled, to about 5 cents on the dollar.

Mark J. Perry and Andrew G. Biggs, writing in The Wall Street Journal, point out that once education, marital status and occupations are considered, the ‘gender wage gap’ all but disappears, The ’77 Cents on the Dollar’ Myth About Women’s Pay:

April 8 is “Equal Pay Day,” an annual event to raise awareness regarding the so-called gender wage gap. As President Obama said in the State of the Union address, women “still make 77 cents for every dollar a man earns,” a claim echoed by the National Committee on Pay Equity, the American Association of University Women and other progressive groups.

The 23% gap implies that women work an extra 68 days to earn the same pay as a man. Mr. Obama advocates allowing women to sue for wage discrimination, with employers bearing the burden of proving they did not discriminate. But the numbers bandied about to make the claim of widespread discrimination are fundamentally misleading and economically illogical.

In its annual report, “Highlights of Women’s Earnings in 2012,” the Bureau of Labor Statistics states that “In 2012, women who were full-time wage and salary workers had median usual weekly earnings of $691. On average in 2012, women made about 81% of the median earnings of male full-time wage and salary workers ($854).” Give or take a few percentage points, the BLS appears to support the president’s claim.

But every “full-time” worker, as the BLS notes, is not the same: Men were almost twice as likely as women to work more than 40 hours a week, and women almost twice as likely to work only 35 to 39 hours per week. Once that is taken into consideration, the pay gap begins to shrink. Women who worked a 40-hour week earned 88% of male earnings.

Then there is the issue of marriage and children. The BLS reports that single women who have never married earned 96% of men’s earnings in 2012.

Christina Hoff Summers has made similar points, No, Women Don’t Make Less Money Than Men:

President Obama repeated the spurious gender wage gap statistic in his State of the Union address. “Today,” he said, “women make up about half our workforce. But they still make 77 cents for every dollar a man earns. That is wrong, and in 2014, it’s an embarrassment.”

What is wrong and embarrassing is the President of the United States reciting a massively discredited factoid. The 23-cent gender pay gap is simply the difference between the average earnings of all men and women working full-time. It does not account for differences in occupations, positions, education, job tenure, or hours worked per week. When all these relevant factors are taken into consideration, the wage gap narrows to about five cents. And no one knows if the five cents is a result of discrimination or some other subtle, hard-to-measure difference between male and female workers.

Even the NY Times acknowledged the obvious back in 2012:

Most economists believe the gap between women’s and men’s wages does not stem primarily from employers paying women less than men for the same job. It occurs mostly because men and women take different jobs and follow different career paths. Part of this difference may be a result of discrimination in hiring and promoting. Much, though, is a result of the constraints of motherhood.

And so did CBS Moneywatch back in 2011:

According to all the media headlines about a new White House report, there’s still a big pay gap between men and women in America. The report found that women earn 75 cents for every dollar men make. Sounds pretty conclusive, doesn’t it? Well, it’s not. It’s misleading.

According to highly acclaimed career expert and best-selling author, Marty Nemko, “The data is clear that for the same work men and women are paid roughly the same. The media need to look beyond the claims of feminist organizations.”

On a radio talk show, Nemko clearly and forcefully debunked that ultimate myth – that women make less than men – by explaining why, when you compare apples to apples, it simply isn’t true. Even the White House report: Women in America: Indicators of Social and Economic Well-Being explains why. Simply put, men choose higher-paying jobs.

That Obama and Democrats continue to campaign on a 100% lie about the 77% pay gap tells you everything you need to know.