Asset bubbles and where to find them

Commentary by Joseph H. Davis, PhD, Vanguard global chief economist

There’s only one sure way to identify an asset bubble, and that’s after the bubble has burst. Until then, a fast-appreciating asset may seem overvalued, only for its price to keep rising. Anyone who has tried to breathe one last breath into a balloon and finds it can accommodate two or three more breaths can relate.

Yale University’s William Goetzmann learned just how hard it can be to pinpoint a bubble. He found that assets whose prices more than double over one to three years are twice as likely to double again in the same time frame as they are to lose more than half their value.1

Vanguard believes that a bubble is an instance of prices far exceeding an asset’s fundamental value, to the point that no plausible future income scenario can justify the price, which ultimately corrects. Our view is informed by academic research dating from the start of this century, before the dot-com bubble burst.

Are there asset bubbles out there now? We at Vanguard have great respect for the uncertainty of the future, so the best we can say is “maybe.” Some specific markets, such as U.S. housing and cryptocurrencies, seem particularly frothy. U.S. home prices rose 10.4% year-over-year in December 2020, their biggest jump since recovering from the global financial crisis.2 But pandemic-era supply-and-demand dynamics, rather than speculative excess, are likely driving the rise.

Cryptocurrencies, on the other hand, have soared more than 500% in the last year.3 It’s a curious rise for an asset that is not designed to produce cash flows and whose price trajectory seems like that of large-capitalization growth stocks—the opposite of what one would expect from an asset meant to hedge against inflation and currency depreciation. Rational people can disagree over cryptocurrencies’ inherent value, but such discussions today might have to include talk of bubbles.

What about U.S. stocks? The broad market may be overvalued, though not severely. Yet forthcoming Vanguard research highlights one part of the U.S. equity market that gives us pause: growth stocks. Low-quality growth stocks especially test our “plausible future income” scenario. For some high-profile companies, valuation metrics imply that their worth will exceed the size of their industry’s contribution to U.S. GDP. Conversely, our research will show that U.S. value stocks are similarly undervalued.

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