In July, the U.S. Department of Labor's Bureau of LaborStatistics released the most recent data highlighting the gap inpay between women and men.

Related: Women will be paid as much as men — in 136years

For all workers, median full-time weekly earnings were $824. Formen it was $909, and for women it was $744, or 81.8 percent ofmedian earnings for men.

Social scientists, economists, lawmakers and equal rightsactivists have been tracking the gender pay gap for decades.Certainly, it has narrowed since President John F. Kennedy signedthe Equal Pay Act into law in 1963, when women earned about 59percent of what their male counterparts did, according to theNational Committee on Pay Equity, a nonprofit advocacy group basedin Washington.

Related: 10 best-paying cities for women

Between 1980 and 2001, the percentage of pay increasedsubstantially, from 60 percent to just over 76 percent. Much ofwhat economists call the traditional rationales for explaining thegender pay gap—such as workforce participation and educationrates—also shifted substantially in that time. In 1963, womenaccounted for 34.4 percent of the workforce; in 1990 it was 45.2percent; by 2015, women accounted for nearly 47 percent of theworkforce.

But since the strides made in the 1980s and 1990s, the incomegap has proven to be stubbornly persistent. In 2007, women earnedabout 78 percent of what men earned. For the next five years, theirpay as a percentage of men's actually dropped marginally.

Meanwhile, the traditional rationales used to, in part, explainthe gap may be providing less ballast for those who challenge thepresence of systemic pay inequality.

Not only are women participating in the labor force at equalrates to men, but in 2015, more women held a bachelor's degree thanmen, marking a first since the Census Bureau began tracking data onhigher education.

Related: Race, gender, make raise negotiations challenging

How much of the gap does sexism explain?

To date, women have failed to reach pay parity in all fields ofemployment. In all 22 industries tracked by the Labor Department,women made less than men in 2014. In some industries the differenceis glaring:

• In the legal field, women make less than 57 percent of what menmake;

• In business and financial operations, they make 75 percent ofwhat men make;

• In management, they make about 78 percent of what men make.

The highest level of parity is in construction, where women make91 percent of what men make—some economists have attributed thelatter to women's increased inclusion in collective bargainingagreements.

All of that data raises the question: How much of the pay gap isattributable to gender bias in the workforce, be it in implicitforms or out-and-out sexism?

Early in 2016, two economists from Cornell University publishedan exhaustive analysis of decades' worth of data exploring the paygap. Beyond labor participation rates and levels of highereducation, the studies attempt to factor how professions tend toattract women, such as nursing and education, and how theiracademic choices—women still study math, science and technology atlower rates than men—affects the wage gap.

The studies also factor time in the workforce, attempting toaccount for the degree to which leaving a job to start a familyaffects women's wages.

That data, and reams of other analysis, can be chalked up to theknowable information economists have used to explain the wagegap.

But to the question of the impact of bias on the wagedifferences between the sexes, economists also account for what iscalled the “unexplained” effect on the gap.

In the “Gender Wage Gap: Extent, Trends, and Explanations,”authors Francine Blau and Lawrence Kahn note that the “unexplained”feature of pay gap analysis has been a standard component of muchof the dissection of the issue over the years.

“Such an unexplained or residual wage gap is often taken as anestimate of labor market discrimination,” write the academics.“However, as is well known, such estimates are suggestive, but notconclusive.”

Over time, the impact of the unexplained—or the potential thatgender discrimination is affecting the wage gap—has decreased, asthe overall pay gap has closed, concluded Blau and Kahn.

Nonetheless, the hard data still fails to fully explain the gap.“The persistence of an unexplained gender wage gap suggests, thoughit does not prove, that labor market discrimination continues tocontribute to the gender wage gap,” just as the decrease in theunexplained gap over time “suggests, though it does not prove, thatdecreases in discrimination help to explain the decrease in thegap.”

Translation: Blau and Kahn presume that discrimination—be itimplicit or out-and-out sexism—has some effect on the wage gap, butless than it likely did in the past.

Obama: Gender pay gap an 'embarrassment'

Others make less diplomatic assessments of the impact of bias onthe wage gap.

During his 2014 State of the Union address, President Obamareferenced the gender pay gap, calling it an “embarrassment,” andadding, “Women deserve equal pay for equal work.”

In an issue brief published in April of 2015 on the pay gap, theWhite House's Council of Economic Advisers acknowledged thedifficulty in taking an accurate measure of bias, but said “thereis little beyond discrimination” to account for economists'“unexplained” portion of the pay gap.

Still, not everyone is convinced of discrimination's impact onthe gender pay gap.

Claudia Goldin, who in 1990 became the first tenured professorin Harvard University's economics department, and whose researchwas frequently cited in Blau and Kahn's research, does not thinkblatant discrimination explains the gender pay gap.

“Does that mean that women are receiving lower pay for equalwork—that is possibly the case in certain places, but by and large,it's not that,” said Goldin, in an interview on the Freakonomicspodcast. “It's something else.”

Goldin suggested those occasions of pure discrimination are“pretty small,” and that the fact that women assume greaterresponsibilities outside the workplace, raising their own familiesand often filling in as care takers for aging parents, explainsmore of the gap.

“The answer is that we don't have tons of evidence that it's(the wage gap) true discrimination,” Goldin told Freakonomics.

Presidential salary

If the gender pay gap were applied to America's highest office,a female president would make $72,800 less than a malepresident.

Lower wages, less for retirement

While economists may disagree on the causes of the pay gap,there is little to dispute the reality that the lower average wageswomen earn will impact their retirement.

Lower earnings translate to lower Social Security benefits,lower accruals in defined benefit plans, and it also makes the 10percent to 15 percent savings rate recommended by financialadvisors more difficult to achieve, given there is less money tosave. In 2014, Wells Fargo found about half of men were enrolled intheir workplace retirement plans, compared to 43 percent of women.When including an employer's match, only 39 percent of women weresaving the 10 percent of their salary.

Complicating those low savings rates for women is the reality oflongevity. Recently updated mortality tables from the Society ofActuaries show the average 65-year-old woman will live 88.2 years,almost two years longer than the average man.

Women need more than 'remedial' financial education

Sallie Krawcheck, co-founder and CEO of Ellevest, a new roboadvisory platform marketed specifically to the needs of womeninvestors, says women's investment needs are different from men's,and women “have not felt welcome” in the traditional financialservices market.

“We certainly do make less—that bugs the crud out me,” saidKrawcheck in an interview with CNBC.

Women currently suffer a major investment gap, says Krawcheck.But the solution is not to wait for the gender income gap to close,nor is it better targeted messaging from Wall Street or gettingmore women “remedial” financial education.

Like other automated investment platforms, Ellevest personalizesan investment strategy, but unlike other robo-advisors, it factorsaverage lifetime salary curves for women, which are different thanfor men.And it incorporates women's risk preferences and longerlifespans, according to the firm's website.

Krawcheck thinks every woman who has retired her high interestdebt should be investing. Ellevest has no minimum account balancerequirements.

For women, investing tends not to be about picking the rightfund or even outpacing broader market indices, according toKrawcheck.

“It's about I want to start a business, I want to retire well, Iwant to have a baby,” Krawcheck said. “How much do I need to getthere and can you put together an investment portfolio to get methere?”