The S&P 500 (SNPINDEX:^GSPC), and the narrower, price-weighted Dow Jones Industrial Average (DJINDICES:^DJI), rose 1.4% and 1.3%, respectively, on the back of a May employment report that did not look strong enough to support an imminent tapering of quantitative easing (bond-buying) by the Fed.

Investors' relief was palpable in the options market, as the VIX Index (VOLATILITYINDICES:^VIX), Wall Street's fear gauge, fell just under 9%, to close at 15.14. (The VIX is calculated from S&P 500 option prices and reflects investor expectations for stock market volatility over the coming 30 days.)

Speaking of volatility, on Monday morning, I wrote that "investors ought to be prepared for some volatility leading up to, and following the release of, Friday's big figure." In this instance, I was correct, as the trailing five-day volatility in the S&P 500 this week was 7.8% (annualized) -- the highest level since April 22nd.

It's not just the magnitude of volatility, either. Over the past several weeks, the market has experienced a bit more downside volatility (i.e. more losing days) than investors had become accustomed to since the beginning of the year. And, while they may have found this unsettling, investors should understand that it is the one-way, lockstep market we have witnessed this year that is unusual -- not the other way around. The following table provides some evidence for this:


S&P 500, % of winning days

2013 (through May 15)


Full history, from Jan. 3, 1950


Source: Author's calculations based on data from Yahoo! Finance.

On a day-to-day basis, the market behaves very much like a random process, so it's not surprising that the ratio of winning to losing days is close to 50:50. Although 11-1/2 percentage points may not seem like much, a ratio that is close to 2:1 is a big departure from this. This is the sort of effect you come across when central bankers are  waving their experimental policy wands.

This morning's employment data suggests we still have some runway ahead of us before the Fed withdraws from the bond market; however, I suspect that the volatility genie is out of the bottle. Investors shouldn't expect as smooth a ride during the second half of the year as they have had so far.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.