FREE NEWSLETTER
WHEN IT COMES to financial decisions, many investors subscribe to an approach known as evidence-based investing. The idea, as the name suggests, is to base decisions, whenever possible, on data rather than on intuition or other informal methods.
This sounds logical. It isn’t perfect, though. Economic and financial indicators have weaknesses which are important to be aware of.
Consider, for example, the Cyclically-Adjusted Price-to-Earnings, or CAPE, ratio, developed by Robert Shiller, a Yale professor and Nobel laureate, along with a colleague. Owing to its pedigree, the CAPE is highly respected. And a study by the Vanguard Group found that the CAPE had the strongest ability to predict market returns among fifteen different metrics it tested. For these reasons, many view it as the gold standard for stock market valuation. But how accurate has it been?
For years, the CAPE ratio has been flashing red. Since 2018, in fact, it’s been more elevated than it was at the peak in 1929, just before the crash. It seems to be indicating extreme risk. And yet, the market has continued to move higher with only temporary setbacks, defying the CAPE’s warnings.
Even Shiller himself has acknowledged that the CAPE’s predictive abilities can fall short. In 2021, he made this seemingly contradictory statement in an opinion piece: “The stock market is already quite expensive,” he wrote, “But it is also true that stock prices are fairly reasonable right now.”
Here’s how he explained this seeming contradiction: While the stock market at the time was expensive by historical standards, he noted that investors should never look at any one metric in a vacuum. Investments need to be considered in comparison to other available options. On that basis, he said, stocks were not expensive, because bonds at the time were also expensive.
Recognizing how the CAPE can register misleading readings under certain conditions, Shiller and a colleague have since developed a modified version of the CAPE called the Excess CAPE Yield. This new metric helps investors compare the prospective relative returns of stocks and bonds. Shiller’s message, in other words: The original CAPE ratio on its own shouldn’t be seen as conclusive.
Another well-respected metric that’s stumbled in recent years is the Sahm rule. In general terms, this rule says that when the unemployment rate begins to increase at a particular rate, a recession is likely. In back-testing, it’s been shown to be remarkably accurate. Since 1959, it would have generated just two false positives.
A few years ago, however, the Sahm rule threshold was breached, theoretically indicating a recession. But Claudia Sahm, the rule’s creator, was quick to explain why investors shouldn’t be nervous. “The Sahm rule is likely overstating the labor market’s weakening due to unusual shifts in labor supply caused by the pandemic and immigration,” she wrote. And in the years since, as Sahm guessed, the economy and the stock market have indeed avoided recession.
The upshot: Economic indicators may work—and even work reliably—for a period of time, but then break down when something about the economy changes in a fundamental or unique way, as occurred in the wake of Covid.
Economic indicators carry another fundamental flaw: In some cases, an indicator might be correct in its prediction but less than accurate in its timing. It might tell us what’s likely to happen, in other words, but won’t tell us when that event is expected to occur. Probably the most famous occurrence along these lines was in 1996, when Alan Greenspan, then the chair of the Federal Reserve, proclaimed that the stock market was exhibiting “irrational exuberance.”
Greenspan turned out to be absolutely right: A bubble was forming in the market, valuations were irrational and a crash was coming. But he didn’t get the timing right. The crash that ultimately occurred didn’t arrive until early 2000—more than three years after he issued his warning. And in those intervening three years, the market more than doubled. Investors who got more cautious in response to the initial warning would have missed out on significant gains.
Along the same lines, consider what occurred with the pandemic. When Covid appeared in 2020, it seemed to arrive completely out of left field with no warning. The reality, though, is that certain experts did have pandemic risk on their radar. A 2019 risk assessment by the Federal Emergency Management Agency (FEMA) highlighted the risk of a pandemic among a short list of concerns. The problem, though, was that the report was vague, describing a risk but without any indication when it might occur. It was like a clock with no hands.
It was because of examples like this that the fund manager Peter Lynch has said, “It’s futile to predict the economy, interest rates, and the stock market…If you spend 13 minutes a year on economics, you’ve wasted 10 minutes.”
That’s humorous, but where does that leave us? On the one hand, we know better than to consult storefront psychics. But economic indicators aren’t terribly reliable either. Investor Howard Marks offers a helpful answer. In his book Mastering the Market Cycle, Marks offers this suggestion: Imagine, he says, a jar filled with a mix of balls of various different colors. No one can tell with the naked eye how many there are of each. But if you can at least have a sense of the mix, that can be helpful. By the same token, no economic indicator should be seen as conclusive, but taken together, they may provide a sense of where things stand.
What does this mean in practical terms? Suppose, for example, you’re considering rebalancing your portfolio and wondering how aggressive to be in reducing risk. You could use Marks’s guideline in this case. If the market seems high, you might be a little quicker to reduce risk. But at the same time, we should always keep in mind the “irrational exuberance” episode as a cautionary tale. It’s a reminder to never veer too far in any one direction. As I’ve suggested before, a center-lane approach often represents the best path forward.
Adam M. Grossman is the founder of Mayport, a fixed-fee wealth management firm. Sign up for Adam’s Daily Ideas email, follow him on X @AdamMGrossman and check out his earlier articles.
