Brendan McDermid/Reuters
- US stocks are one week into what's historically been their worst month of the year, in what is known as "The September Effect".
- The S&P 500 is currently down about 1% so far this month.
- Market veteran Ed Yardeni has highlighted some of the key risks facing investors this time around.
US stocks are one week into what's historically been the worst month of the year for the