The long-term returns of private equity have slipped behind the public stock markets for the first time in 30 years, according to new figures — adding to concerns that private equity firms are paying too much to buy companies, leading to lacklustre profits in future.

Over the past 10 years, US buyout funds on average returned 15.3% compared with the S&P 500’s 15.5%, according to according to Bain & Company’s Global Private Equity Report 2020. That has upended an advantage established in prior decades, with US buyouts ahead of the public market by 13.1% to 8.1% on average over the past 30 years.