CHART OF THE DAY: Septembers Are The Worst

When it comes to the stock markets, history is a guide but never gospel.

In his latest weekly Macro View comment, Guggenheim Partners' Scott Minerd offers this interesting bar chart of average monthly stock market returns.

"Historically, September is the worst month for U.S. stock market performance," wrote Minerd. "Since 1929, the S&P Composite Index has averaged -1.1 percent for September, making it one of only three months with negative average returns over that time. The worst performing single month over this time period was September 1931, when the S&P composite fell 30 percent."

This year, September promises to bring uncertainty.

"There are several macroeconomic uncertainties facing the United States and the global economy as we head into September," continued Minerd. "The potential tapering of the U.S. Federal Reserve’s asset purchase program, the budget debate in Washington, and the German election could all increase volatility in global financial markets."

But more often than not, its the unknown uncertainties that do the real damage.