‘Sleepwalking’ Markets Woke Up This Year. That’s a Good Thing.

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If 2018 feels volatile to stock investors, it may be a reflection of how placid 2017 was.

The S&P 500 closed up 1.6 percent Monday. It marked the 53rd day the index has risen or fallen 1 percent or more this year. Including Monday’s gain, 17 of those moves have come since the start of October, when concerns about trade, slowing global economic growth and higher interest rates began to batter stocks.

That’s not far from how things usually go with stocks. Since 1928, the S&P 500 has averaged 62 days of moves that were 1 percent or greater per year, according to data from Howard Silverblatt, senior index analyst for S&P Dow Jones Indices.

But 2018’s moves do represent a significant uptick from 2017, when stocks steadily climbed higher in anticipation of a cut to the corporate tax rate. Last year, there were just eight days in which stocks rose or fell by 1 percent or more. That’s the lowest number in at least 15 years, Mr. Silverblatt said.

Many stock market watchers view the return of volatility as healthy, claiming it serves as a reminder that investing is risky and markets don’t just march higher. That can help prevent bubbles from forming.

“It only feels abnormal because investors and market pundits anchor their expectations on the recent sleepwalking past,” said Nicholas Colas, the co-founder of DataTrek Research.