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In technical analysis, a measure of a security's volatility in a downward direction. That is, the Ulcer Index is a measure of the depth and duration of a security's downward trend. The UI is thus a measure of a security's risk. The higher a security's rating on the UI, the more risk it carries. It was designed as a corrective to measurements of standard deviation, which, according to proponents of the UI, does not adequately calculate risk.