The Short Interest Ratio (SIR) measures investor sentiment for a given company and is calculated using the number of shares being shorted divided by the average daily trading volume of the stock.
Also called the short ratio or float short, the SIR is a ratio of the number of shares being shorted divided by the average daily trading volume for the stock over the last 30 days. The ratio can be interpreted as the number of days it takes short sellers to repurchase borrowed shares, or an approximation for the number of shares that have been sold short and not yet covered as a percentage of all trading volume.
An SIR for an entire exchange can be calculated to gauge market sentiment. Low short interest ratios should be taken as a bullish indicator, and vice versa.
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