James O’Shaughnessy says to block out the noise and listen to what history has to say about where the stock market is headed — upward.

“We need perspective on the markets, and that’s something we sorely lack today,” O’Shaughnessy told MarketWatch after giving a presentation at The Big Picture Conference. He says that just to match the worst 20-year period in history, stocks will have to rise between 30% and 50% by 2020. And, he says, “I don’t think we’re going to match the worst 20-year period [we’ll likely do better]. … When we look at those previous periods, their problems were far more impactful than what we see today.”

O’Shaughnessy said his tactical asset allocation portfolio has 55% of its money in stocks, 19% in real estate investment trusts, and 16% in high-yield bonds. He says things may get choppy for stocks in the short term, but says “that’s absolute noise”. The outlook for the next several years is positive, he says. “Yes there are always possibilities,” he said, referring to potential pitfalls, “but I look at probabilities.”