The change came in US stock market after 1980

Pessimism appeared to be setting in the days running up to Monday 19 October.
Both the Dow Jones and the S&P 500 had lost more than 9% over the week by the time markets closed on Friday 16 October.
That loss had Asian investors playing catch-up when they opened for business on Monday.
And as more markets opened, that selling activity in Asia sparked more selling in Europe, leaving the US playing catch-up with the losses it had originally inspired.
By the end of the day, the Dow Jones had fallen by more than 20% and the UK's FTSE 100 by 11%.
It ended up as the steepest crash since 1929.
Dow chart
"Our mouths were wide open, our jaws were hitting the desk," says Peter Borish, who at the time was second in command at Tudor Investment Corp, a US hedge fund.
Tudor was one of the few firms to predict the crash and ended up turning a profit by innovative use of computer modelling.
"Fear always trumps greed and fear was at its maximum point then, so when people are fearful rationality goes out the door and they just start selling."