What it means
Ulcer Index is a risk metric that quantifies the 'ulcer-inducing' pain of an investment by combining drawdown depth AND duration. Formula: square root of mean squared drawdown over a lookback period. Unlike volatility, UI doesn't penalize upside; unlike max drawdown, UI captures multiple drawdowns. Used heavily by trading systems literature (Peter Martin) for evaluating systems that produce extended drawdowns.
Why it matters
Two strategies can have identical max drawdown but very different drawdown experiences — one with one big drawdown that recovers in weeks vs another with months of grinding decline. UI distinguishes these. The latter is much harder to trade emotionally; UI captures that.
How to use it
Compute UI over 3+ years (longer is more stable). Lower UI = smoother drawdown experience. Compare UI across strategies as a complement to max drawdown — a system with lower UI but slightly higher max DD is often preferable because the experience is more recoverable.
Want a worked example or a deeper dive? Ask Rocky how this concept applies to your specific watchlist or trade idea.
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