As Donald Trump never tires of boasting, the US stock market is enjoying an extraordinary boom. Last year the S&P 500 recorded its first perfect calendar year of monthly total returns. But the bull run has failed to soothe one of the biggest and most intractable conundrums on Wall Street: the dearth of companies going public.

Last year was a respectable one in the US for initial public offerings. According to Dealogic, 189 companies floated on the US stock market and raised nearly $50bn, almost twice the amount in 2016, a particularly poor year. Last year’s showing has provided hope but concerns remain.

In the 1980s, the US averaged more than 200 IPOs a year, and during the dotcom boom — when the focus was on going public quickly on a prospectus of ideas and enthusiasm rather than a record of success — US markets saw 547 listings in 1999 and 439 in 2000. Now companies seem to delay going public indefinitely rather than listing too soon.