Volume is simply the number of shares (or contracts)
traded during a specified time frame (e.g., hour, day, week, month,
etc). The analysis of volume is a basic yet very important element of
technical analysis. Volume provides clues as to the intensity of a given
price move.
Interpretation
Low volume levels are characteristic of the
indecisive expectations that typically occur during consolidation
periods (i.e., periods where prices move sideways in a trading range).
Low volume also often occurs during the indecisive period during market
bottoms.
High volume levels are characteristic of market tops
when there is a strong consensus that prices will move higher. High
volume levels are also very common at the beginning of new trends (i.e.,
when prices break out of a trading range). Just before market bottoms,
volume will often increase due to panic-driven selling.
Volume can help determine the health of an existing
trend. A healthy up-trend should have higher volume on the upward legs
of the trend, and lower volume on the downward (corrective) legs. A
healthy downtrend usually has higher volume on the downward legs of the
trend and lower volume on the upward (corrective) legs.
Example
The following chart shows Merck and its volume.
Prices peaked at the end 1991 following a long
rally. This was followed by a price decline (trendline "A1"). Notice how
volume was relatively high during this price decline (trendline "A2").
The increase in volume during the price decline showed that many
investors would sell when prices declined. This was bearish.
Prices then tried to rally (trendline "B1").
However, volume decreased dramatically (trendline "B2") during this
rally. This showed that investors were not willing to buy, even when
prices were rising. This too, was bearish.
This pattern continued throughout the decline in
1992 and 1993. When prices rallied, they did so on decreased volume.
When prices declined, they did so on increased volume. This showed,
again and again, that the bears were in control and that prices would
continue to fall.