---
description: "Buys stocks with the largest monthly increases in call implied volatility and shorts stocks with the largest increases in put implied volatility, exploiting the options market's directional information."
tags: [stocks, implied-volatility, options-based]
---

# Implied Volatility

**Section**: 3.5 | **Asset Class**: Stocks | **Type**: Options-Based / Signal

## Overview
This strategy is based on the empirical observation that stocks with larger increases in call implied volatilities over the previous month have higher average future returns, while stocks with larger increases in put implied volatilities over the previous month have lower average future returns. The options market contains forward-looking information about stock direction that can be exploited cross-sectionally.

## Construction / Signal
The signal is the monthly change in implied volatility for calls and puts separately:

- **Call IV change**: `Delta_call_IV_i` = change in call implied volatility for stock `i` over the previous month
- **Put IV change**: `Delta_put_IV_i` = change in put implied volatility for stock `i` over the previous month

**Primary portfolio construction**:
- Buy stocks in the **top decile** by increase in call implied volatility (large call IV increases → bullish signal)
- Short stocks in the **top decile** by increase in put implied volatility (large put IV increases → bearish signal)
- Dollar-neutral construction.

## Entry / Exit Rules
- **Entry**: At monthly rebalance, rank stocks by their respective IV change signals and enter positions as described.
- **Exit**: Hold for approximately 1 month before rebalancing.

## Key Parameters
- **Lookback**: 1 month for IV change computation
- **Holding period**: Typically 1 month
- **Portfolio construction**: Dollar-neutral long/short

## Variations
- **Difference signal**: Instead of two separate portfolios (long high-call-IV, short high-put-IV), construct a single signal based on the *difference* between the change in call implied volatility and the change in put implied volatility:
  ```
  Signal_i = Delta_call_IV_i - Delta_put_IV_i
  ```
  Buy top-decile by this difference, short bottom-decile.

## Notes
- Requires options market data (implied volatility surfaces or at-the-money IV for calls and puts).
- The empirical evidence suggests options markets reflect informed trading that leads equity prices.
- Transaction costs in options markets can be high; the strategy operates on stock positions, not option positions.
- Monthly rebalancing is typical given the 1-month signal horizon.
- Can be combined with other momentum or factor signals in a multifactor framework.