September got off to a rocky start yesterday as the Dow Jones Industrial Average lost 2%, stoking fears concerning what has historically been the worst month in the calendar for stocks. But just how bad could things get this year?

A short market history lesson
Using price data from Dow Jones going back to May 1896, I verified that September is indeed the worst month for the Dow on the basis of average returns. At (1.2%), it is one of only two months that can't boast a positive average return (the other is February, with a much smaller 0.2% loss). September also hosted the worst monthly performance for the Dow in history: a loss of nearly 31% in 1931.

That was then, what about now?
What can we expect this year? A month's time horizon is far too short to even begin making a serious prediction. However, according to data compiled by Professor Robert Shiller of Yale, the broader S&P 500 index is valued at nearly 18 times its cyclically-adjusted earnings (average inflation-adjusted earnings over the prior 10 years). That is a premium to the multiple's long-term historical average of 16.3, so a correction of 10% to 20% wouldn't be highly surprising in this environment.

The good news
The outlook isn't uniformly somber, though: By my calculations, every one of the Dow components is currently changing hands at a cyclically-adjusted P/E multiple below that of the S&P 500. This includes superb businesses such as:


Cyclically-Adjusted P/E Multiple*

Caterpillar (NYSE:CAT)


Exxon Mobil (NYSE:XOM)


Walt Disney (NYSE:DIS)


JPMorgan Chase (NYSE:JPM)


United Technologies (NYSE:UTX)


Microsoft (NASDAQ:MSFT)


Cisco Systems (NASDAQ:CSCO)


*Note that the calculation of these multiples isn't perfectly consistent with Shiller's calculation for the S&P 500.
Source: Author's calculations, based on data from Capital IQ, a division of Standard & Poor's.

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Alex Dumortier, CFA, has no beneficial interest in any of the companies mentioned in this article. Walt Disney is a Motley Fool Stock Advisor recommendation. Walt Disney and Microsoft are Motley Fool Inside Value selections. The Motley Fool has a disclosure policy.