The pay gap between men and women in the US is real, but predominately caused by fewer women than men in higher-paying roles, according to research released by executive search firm Korn Ferry International Inc. (NYSE: KFY). The Korn Ferry Gender Pay Index analyzed gender and pay for more than 1.3 million employees in 777 companies in the US, drawn from Korn Ferry’s PayNet database.

The data found women earn nearly 20% less than men as a whole. However, that gap is significantly reduced when comparing women and men in the same jobs.

“This pay gap issue can be remedied if organizations address pay parity across the organization and continue to strive to increase the percentage of women in the best paying parts of the labor market, including the most senior roles and functions such as engineering and technical fields,” said Korn Ferry Senior Client Partner Maryam Morse.

The index found that when comparing pay between genders overall in the US, men are paid 17.6% more than women, which is in line with research from the Bureau of Labor Statistics. However, the gap fell to 7% when evaluating the same job level, such as director. The gap tightened to 2.6% when considering the same level at the same company; when male and female employees at the same level and the same company worked in the same function, the average gap was less than 0.9%.

Korn Ferry released the index in advance of Equal Pay Day, which takes place April 10. The date symbolizes how far into the year women must work to earn what men earned in the previous year. The National Committee on Pay Equity launched the event in 1996 as a public awareness event to illustrate the gap between men’s and women’s wages.