As September is coming to a close, the S&P 500 looks set to post another monthly gain. However, most of that gain came completely on two trading days: September 6th and 13th when Mario Draghi and Ben Bernanke each announced infinite monetary action. Without those two days the S&P 500 would be 52 points lower and the chart would look like it does below.
Of course, it's not really possible to strip away two trading days or the effect of what that news did to prices. However, the hypothetical chart below does highlight that there have been more down days than up days in September.