The Negative Volume Index ("NVI") focuses on days
where the volume decreases from the previous day. The premise being that
the "smart money" takes positions on days when volume decreases.
Interpretation
The interpretation of the NVI assumes that on days
when volume increases, the crowd-following "uninformed" investors are in
the market. Conversely, on days with decreased volume, the "smart money"
is quietly taking positions. Thus, the NVI displays what the smart money
is doing.
In Stock Market Logic, Norman Fosback points out
that the odds of a bull market are 95 out of 100 when the NVI rises
above its one-year moving average. The odds of a bull market are roughly
50/50 when the NVI is below its one-year average. Therefore, the NVI is
most usefuly as a bull market indicator.
Example
The following chart shows Avon and its NVI. I drew
"buy" arrows whenever the NVI crossed above its 1-year (255-trading day)
moving average.
I drew "equal-signs" when the NVI fell below the
moving average. You can see that the NVI did a great job of identifying
profitable opportunities.
Calculation
If today's volume is less than yesterday's volume
then:
If today's volume is greater than or equal to
yesterday's volume then:
Because falling prices are usually associated with
falling volume, the NVI usually trends downward.