Mark Robertson, whose market projections have been quite accurate over the past four years, says the next four years are likely to be slightly below average for the stock market.

According to MarketWatch’s Mark Hulbert, Robertson’s model is based on the projections of Value Line analysts regarding the total returns that 1,700 widely followed stocks will produce over the next three to five years. “To adjust for analysts’ (if not humans’) tendency to be overly optimistic, Robertson focuses on the low end of the range of the three-to-five-year return projections for each stock,” Hulbert explains. “He then uses the average of those projections to forecast the stock market’s return over the next four years.”

Four years ago, Robertson’s model was projecting annualized returns of nearly 20%, Hulbert says — at a time when many thought such returns were impossible. But since then, the market has returned about 23% annualized. Now, he’s projecting annualized returns of 8.2% over the next four years — just below the 8.5% average for the past two decades, and a couple points below the last century’s 10% to 11% returns.

Robertson says the appropriate response to such a forecast is not to flee the market, but to “scale back” on speculative picks and “begin to focus on higher quality stocks,” Hulbert writes. For those with a big lump sum to invest, he recommends investing about 60% to 70% of it now, and keeping 30% to 40% in cash.