A “new measure of market fear” indicates that investors might be more skittish than the current volatility gauges suggest, according to a recent article in The Wall Street Journal.

The article reports: “The gauge of so-called ambiguity, meant to chronicle the degree of uncertainty investors have in the probabilities they use to make decisions, has been at all-time highs in recent months, indicating that there’s more fear built into the stock market than common measures of volatility suggest.”

In October, the gauge reached 2.42, it’s highest reading since 1993, the article says, noting that it hit 2.41 in October 2008 (at the height of the financial crisis). The CBOE Volatility Index (VIX), on the other hand, has declined this year—a trend that the article says has “befuddled investors and traders of all stripes, given the host of geopolitical uncertainties in locations like North Korea and political skirmishes in Washington.”

According to Menachem Brenner of New York University, a pioneer in volatility research, ambiguity tends to track rises in the market. The higher stock prices get, that is, the more uncertainty investors feel about the future. “In that sense,” the article says, “the high levels of ambiguity don’t necessarily suggest an imminent decline in the stock market.”