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STORY: Although the S&P 500 is down more than 5% from its March 28 closing high, Stovall advised investors stay calm, despite his belief that stocks may "still have more downside to go."

"When it comes to market timing," he explained, "you're better off not worrying about it. Because if you count up all of the declines of 5% or more since World War II, nearly 90% of them have been declines of 5 to 20%. And on average, it's taken only four months to get back to break-even. So in the time that you've worked yourself up into a frenzy, harassed your advisor to lighten up your equity exposure, by that time the market is probably already on its way to break-even."