An index of market uncertainty is at a two-year high

THE VIX, or “fear index,” rose to 26.25 percentage points on October 15th, reaching its highest level since a crisis over the fate of the euro currency in 2012. When markets smell trouble, the metric spikes. Specifically, the VIX tracks how much investors willing to pay to insure against sharp movements of the S&P 500 to move in the next 30 days: higher options prices imply higher volatility (and thus a higher VIX). Similar indices for gold, oil and emerging-market shares have been just as effervescent.

The recent unease escalated on October 7th when the International Monetary Fund lowered its world economic forecast for the third time this year. Other market concerns include the spread of Ebola and a collapsing oil price. The soaring volatility ends an eerily long period of calm in the marketplace. The index averaged 13.8 percentage points over the past two years, well below the long-run historical average of 20. Yet for investors, it marks a return to their customary jitteriness.