According to one dependable valuation model, writes Mark Hulbert in a recent article for MarketWatch, stocks are now more overvalued than they have been since 1969.

The model Hulbert cites is based on Value Line’s Median Appreciation Potential (VLMAP), a number published weekly by Value Line, Inc. that represents the median of the projected valuations (in three to five years’ time) of 1,700 stocks monitored by the firm’s analysts.

Hulbert says that a number of academic studies have found that “VLMAP can be profitably used as a market-timing tool. The model calls for increasing your exposure to the stock market when it is at well-above-average levels and decreasing exposure when—as it is now—it’s well below average.” The VLMAP is currently at 20% while, at the bottom of the bear market in March 2009, it stood at 185%.

The article points out, however, that the VLMAP has been low for quite some time, and the stock market could continue to rise despite these depressed levels. “But the evidence of overvaluation continues to accumulate,” Hulbert adds. “Someday, the sheer weight of that evidence will be too much for even this bull market to bear.”