A ratio that divides volume on up days by volume on down days to test whether real demand sits behind a trend. It exposes which side the crowd actually committed its money to, not just where price went.
The Up/Down Volume Ratio (UDVR) divides the total volume that traded on up days by the total volume that traded on down days over a chosen period.
The idea is plain but sharp. When price rises on heavy volume, money is backing the advance. When volume swells mostly on the days price falls, participants are rushing to sell.
So this ratio compresses into a single number not just the direction of a trend, but how hard the crowd actually bet on that direction.
William O'Neil popularized it as a tool for gauging institutional sponsorship in individual stocks. Across the whole market, the same idea is used as a breadth measure: total volume in advancing issues divided by total volume in declining issues.
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