The risk of a US stock market correction viewed from the bond market
US equities have been very expensive for a long time when judged using simple measures of long-term valuation.
In valuing equities against bonds, US equities have historically paid a large risk premium above the risk-free rate, but this premium is currently at a historically low level, albeit not at the extremes of the dot-com bubble.
Defining the equity risk premium as the difference between the forward earnings yield and the real government bond yield*, the premium for the S&P 500 has averaged 4.6pp over the almost forty years for which data are available (the premium for the Nasdaq has averaged 3.6pp over the past twenty-five years for which there are data).
The equity risk premium for the S&P in October was well below this average at 2.9pp (or 2.1pp for the Nasdaq), although it has been around this low level for a couple of years now (or a few years in the case of tech stocks).
By design, these long-term metrics are not meant to provide a timing signal for the market, although, to provide an insight into what a sustained stock market correction could look like, the S&P 500 would have to fall by about a quarter to return the equity risk premium to its average level assuming broadly no change in earnings (about the same for the Nasdaq).
Realistically, though, in a scenario of a sustained stock market correction, a return to a more normal equity risk premium would also involve lower bond yields.
Note: * the 10-year real bond yield is the median of a number of estimates.
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