I had asked this in earlier post. Marginal Revolution in Piling on Samuelson says that Samuelson needs to do his homework. I questioned Krugman's theory on Econbrowser but I got no evidence either. Here was Krugman's theory:
Instead of investing in physical capital, many companies are using profits to buy back their own stock. And cynics suggest that the purpose is to produce a temporary rise in stock prices that increases the value of executives’ stock options, even if it’s against the long-term interests of investors.
It’s not a far-fetched idea. Researchers at the Federal Reserve have found evidence that ... stock buybacks are strongly influenced by “agency conflicts,” a genteel term for self-dealing by corporate insiders. ...
Whatever the reasons, we now have an economy with incredibly high profits and surprisingly low investment.
I was hoping to find some information on stock buybacks (that doesn't require me to pay a lot for it). The suggestions in the comments section of Econbrowser didn't lead to anything useful.