The predominant investing mantra nowadays is to pick some nice index funds and stick with them, since you can’t know when the market is going to go up or down. In this appropriately titled book Yes, You Can Time The Market!, Ben Stein and Phil DeMuth argue against that. Instead of using fundamental valuation, where someone tries to analyze a company and find it’s “true” value vs. market value, they argue that a market index as a whole, such as the S&P 500, can be viewed as cheap or expensive by comparing it against it’s 15-year moving historical average.
For example, you can take the average of the P/E ratio of the S&P 500 for the last 15 years. If the current P/E ratio is greater than that average, then it is overvalued. If the current P/E ratio is less, then it is undervalued, a signal to buy. (Right now it’s 25 vs. 19, undervalued.)
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