Number of S&P 500 female CEOs decreased in 2015

WASHINGTON, Dec. 29 (UPI) -- The amount of female CEOs in S&P 500 companies decreased in 2015 as the United States continues to trail global competitors in terms of gender equality

Women ran 21 S&P 500 companies in 2015, down from 25 in 2014. Though there was a decline in the past year, the number increased from 16 in 2005. Meanwhile, 96 percent of S&P 500 companies were run by men in 2015, down from 97 percent in 2006.

The decline of women at the helm comes amid evidence that women generally outperform men in top executive positions, NBC News reported.

"Despite all of the attention placed on increasing the number of female executives at American companies, the needle on the gender gap has hardly moved," Pavle Sabic, director of market development at S&P Capital IQ, wrote in the "How Times Have Changed? CEO Gender Gap Analysis of the S&P 500" study. "The gender gap at the CEO level of S&P 500 companies is not closing. Growth rate for new female CEOs is only one per every two years."

The United States is ranked 20th out of 140 countries in the World Economic Forum's 2014 Global Gender Gap Report between Canada (19) and Ecuador (21). Iceland (1), Finland (2) and Norway (3) lead the list.

A study earlier this year from the Bespoke Investment Group found that share performance by companies run by female CEOs had been topping male-run companies by 5 percentage points. Female-run companies in 2015 averaged returns of 0.19 percent, compared to the S&P 500 index price decline of nearly 2 percent.

Women tend to be CEOs for shorter periods of times, averaging four years compared to six years for men.

"While four to six years is not largely significant in the context of a lifelong career, it may translate to a significant economic opportunity cost to women," Sabic adds.