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Why leaving your desk this August may be a risky move

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August was traditionally the month when market players put on their out of office (or in an earlier era their voicemail) for a couple of weeks and sidled away from their desk.

Yet whether they're in the Hamptons, Positano or Cannes, it's going to be difficult to ignore markets as the August effect of stock market volatility looks to be back with a bang.


Just this week, the price of oil (as measured by Brent crude) fell to a five-month low of $42.69, the Dow Jones Industrial Average hit the feared "death cross" and Chinese markets have been rocked by measures to weaken the yuan.

The August effect seems to be a relatively recent phenomenon, but it has been more pronounced since the sub-prime mortgage crisis first came to light in August 2007. The S&P 500 has posted losses in three of the last five Augusts, but if you stretch this out to the last 15 years, it has registered gains 10 times.

Fewer people at their desks can mean that market swings become more accentuated, which may be why August has the second-highest volatility rate of any month, after October.

Recent August heart-in-your-mouth moments include: the bailout of the Irish banking system (2010), the U.S. debt ceiling crisis of 2011, and this year's unexpected Chinese turmoil. There could be worse to come if, as some market historians are warning, there are signs of divergence pointing to a top in the market.

"In the US today, we are seeing a significant disconnect between the large-caps (e.g. SPX, NDX) and the smaller companies found in the Russell 2000 and the Nasdaq Composite. And this divergence pattern is indeed worrisome. Historically, we have seen some significant tops form from such "lethal divergences," Hayes Martin, president of investment consulting firm Market Extremes focused on market turning points throughout history, told CNBC.


However, he doesn't think it is all about August.

"Concerning the 'August' effect, this to me has little meaning any more. Many of the old traditional patterns are being broken today, as the stock market is now so globally interconnected," Martin said.

And whatever you think of August, at least it's not September. Now there's a month we can all agree is awful.

- By CNBC's Catherine Boyle