Some have argued that the wage gap, at any stage of a woman's life, starts with her choices. Women are more likely than men to scale back at work when they start a family, for instance. But the EPI data shows that the gender wage gap cracks open right after college graduation, well before decisions like maternity leave can affect women's earnings.
The gender wage gap in the broader labour force has steadily declined since the 1980s.
"It is noteworthy that stark wage disparities between men and women occur even at this early part of their careers," the researchers wrote, "when they have fairly comparable labour market experience."
Young men with a college degree earn an average hourly wage of $20.94 right after graduation, according to the EPI figures, compared with the average hourly wage of $16.58 for women. That's a $9,000 annual difference.
Teresa Kroeger, co-author of the paper, said rising wages for men at the top of the income distribution appear to be exacerbating the chasm. "We suspect this is following the overall trend of the economy," she said.
Men tend to dominate the workforce in the highest-paid career fields such as technology and finance, Kroeger said. There has been more wage growth in these fields over the past year as pay in others has stagnated. That may explain part of the ballooning gap.
It's not clear, however, whether chosen jobs and fields are driving the wage gap for young workers.
A recent analysis of Bureau of Labor Statistics data by the PayScale website broke out jobs where at least 85 per cent of the workers are men and at least 85 per cent of the workers are women.
The top three male-dominated occupations (software developer, computer systems administrator and construction project manager) all offered higher average pay, the study found, than the top three female-dominated occupations (elementary school teacher, registered nurse and human resources specialist.) The average income for a 22-year-old man in the study was $40,800, compared with $31,090 for a 22-year-old woman.
Kevin Miller, a senior researcher at the American Association of University Women, said choice is just one determining factor in workers' pay.
"Men in, say, engineering and computing are getting the majority of those degrees," he said, "but women also face gender norm barriers and harassment in those fields. It's not always a choice free of constraints."
Although discrimination is difficult to prove, research offers insight into how women may encounter it.
In one infamous 2012 study, science faculty from research-intensive universities assessed fake résumés from male and female candidates for a laboratory manager position. Although the fictional students' qualifications were identical, the faculty members routinely ranked the men as more qualified for the job.
A 2015 AAUW report of workers one year out of college found considerable pay differences between men and women in the same career fields.
Women who majored in business, for example, earned an average of $38,000, while men bagged just more than $45,000. In engineering, computer and information sciences fields, young female graduates earned between 77 per cent and 88 per cent of what their male colleagues made.
Across all fields, after controlling for major, occupation and grade-point average, the report found women still earned 7 per cent less than men.
