Historical vs. Implied Volatility
Historical (realized) volatility measures how much a stock's price actually moved over a past period, typically calculated as the standard deviation of daily returns annualized. A stock with 30% annualized volatility means its daily moves average roughly 1.9% (30% / sqrt(252)).
Implied volatility is forward-looking, derived from options prices. It represents the market's expectation of future volatility. When implied volatility is higher than historical, the market expects larger moves ahead.
The VIX: Market Fear Gauge
The CBOE Volatility Index (VIX) measures implied volatility of S&P 500 options over the next 30 days. It is often called the "fear gauge" because it spikes during market stress.
Historical VIX ranges provide context. Below 15 represents complacency or calm markets. Between 15-25 is considered normal. Above 25 indicates elevated anxiety. Spikes above 35-40 typically accompany significant market dislocations.
The Apter Market Data page includes VIX levels as part of its risk signal assessment.
Volatility and Risk
In finance, volatility is the standard proxy for risk. Higher volatility means wider distribution of potential outcomes — both positive and negative. A volatile stock can deliver exceptional gains but can also inflict severe losses.
Importantly, volatility is symmetric: it measures movement in both directions. A stock that frequently gaps higher is volatile, even though those moves are favorable. Risk-adjusted return metrics like the Sharpe ratio account for this by measuring return per unit of volatility.
Volatility Regimes
Markets alternate between low-volatility and high-volatility regimes. Low-volatility regimes tend to persist until an external shock triggers a regime change. High-volatility regimes tend to cluster: once volatility spikes, it typically remains elevated for weeks to months before gradually subsiding.
This clustering behavior means that positioning should account for the current regime. The Apter Risk factor incorporates 30-day realized volatility relative to the stock's own historical norms.