The Negative Volume Index (NVI) was developed by Paul Dysart and is used by traders to identify bull and bear markets by following the smart money. It uses volume data to identify which price moves are caused by this money. The assumption behind the indicator is that smart money requires less volume to move price. It goes up when price goes up on low volume and goes down when price goes down on low volume. It remains unchanged when volume is high, assuming that's when the crowd is active. The indicator is the opposite of the Positive Volume Index (PVI) which aims to identify price moves when the crowd is active. It is best used in combination with other analysis techniques.