To many people, the terror of falling share prices is often significant, often more so than the pleasure of gains. Accordingly, investors often want to minimize downside volatility as a part of their portfolio planning. Investors already have several tools to measure downside volatility, including the lower partial moment and the maximum drawdown. The performance benchmarks use the lower partial moment as a risk measure. The lower partial moment, however, doesn’t entirely describe the panic of investors facing continuously falling stock prices, and the maximum drawdown only captures a single event. A different tool is needed. Developed by Peter Martin in 1987, the Ulcer Index measures the human stress of holding a stock. Ulcer Index is a volatility measure that only captures continuous downside movements in share price, and ignores upside volatility. The more continuous and prolonged the drawdown, the higher the index and the more likely investing in it will cause ulcers or sleepless nights.