A measurement used to estimate the strength of market movement based on the ratio of the volume of trades in up stocks vs. the volume of trades in down stocks. The ratio is found by dividing the volume in up stocks by the volume in down stocks for a given time period (daily, weekly, etc). If 30 million shares are moving up while 10 million shares are moving down, the ratio is 3:1. The higher the ratio of up to down and the more the ratio increases in that direction over time, the more bullish the market.