They show that the number of stock market-listed companies in the US has fallen in recent years - from over 7,000 in 1995 to less than 3,800 last year. What's more, the companies that are listed now are very different from those that were on the market 20 or 40 years ago. Companies today, they show, are bigger and older than they were then; are less profitable; invest less in machinery; and hold more cash.
What explains these changes?