Positive Volume Index: Crowd Flow on Busy Sessions

Key Takeaways

• PVI moves only on days when today's volume is greater than the previous day's volume.
• Fosback's version updates by the percentage change in close on each qualifying day.
• The classic signal compares PVI to its 255-day moving average, with the rule weighted toward bearish confirmation.
• The most common misreading is treating PVI as a momentum indicator on quiet sessions, when by construction it does not change.

What It Is

The positive volume index PVI is the companion line to the negative volume index. Both originate from Paul Dysart's 1930s breadth work, but Fosback adapted them for price-based charts.

PVI is plotted just like OBV, a cumulative line below price. The difference is the trigger: PVI updates only when volume increases, and stays flat otherwise. The result is a series that tracks what happens on louder, more news-driven sessions.

The Intuition

Fosback argued that retail or "uninformed" money tends to dominate volume on busy days, when news is hitting and the public is reacting. Volume spikes on earnings, macroeconomic surprises, or media coverage often pull crowd participation into the tape.

If that is right, then a line that only follows price changes on heavy-volume days captures crowd behavior. PVI is exactly that line. Where NVI is treated as a smart-money proxy, PVI is treated as a crowd-flow proxy.

How It Works

PVI is computed with a simple branch each bar:

If Volume > Prior Volume:
    PVI = Prior PVI + Prior PVI * (Close - Prior Close) / Prior Close
Else:
    PVI = Prior PVI

The starting value is arbitrary, often 1000. Once enough history accumulates, PVI is plotted against its own 255-day simple moving average. The Fosback reading is:

• PVI below its 255-day SMA: high probability that a bear market is in progress.
• PVI above its 255-day SMA: less reliable as a bull signal, since busy-day participation is noisier.

The asymmetry is deliberate. Fosback's historical work indicated that PVI is more useful as a bearish confirmation than as a bullish one. That is the mirror image of NVI's interpretation.

Worked Example

Begin with PVI at 1000. Track six bars:

• Day 1, baseline
• Day 2, volume rises, close +2 percent: PVI updates to 1020
• Day 3, volume falls, close any change: PVI stays at 1020
• Day 4, volume rises, close -1 percent: PVI updates to about 1009.8
• Day 5, volume rises, close +0.5 percent: PVI updates to about 1014.85
• Day 6, volume falls: PVI stays at 1014.85

The line walks based only on the price changes during the busy sessions. Quiet sessions leave it untouched.

If after several months PVI drifts below its 255-day SMA while broader trend metrics also weaken, the Fosback rule flags an elevated probability of an ongoing bear phase.

Common Mistakes

1. Using PVI alone for entries. It is a regime confirmation tool, not a timing signal. Pair it with trend and breadth measures.
2. Treating the bull reading as strong. Fosback's empirical work assigned more weight to PVI below its SMA as bearish confirmation than to the upside cross as bullish confirmation.
3. Confusing PVI with PVT. Price Volume Trend uses all bars and scales volume by percentage change. PVI uses only volume-up bars and the full percentage change. Different mechanics, different readings.
4. Ignoring volume distortions. Quadruple witching, index rebalances, and earnings can produce volume spikes unrelated to ordinary participation. They still trigger PVI updates.
5. Plotting PVI without its 255-day SMA. The cross with the SMA is the actual published signal; the raw line on its own is hard to interpret across regimes.

Frequently Asked Questions

What is the positive volume index PVI in simple terms? The positive volume index PVI is a running total that updates only on days when volume rises, intended to track what crowd-driven trading is doing on the loudest sessions.

How does the positive volume index PVI affect investment decisions? Investors use PVI crossing below its 255-day moving average as a confirming bear-market signal. Above the SMA, PVI is treated as supportive of risk-on conditions but less decisively bullish.

What is a real-world example of the positive volume index PVI? Heading into a sustained equity selloff, broad market PVI lines often slip beneath their 255-day SMAs while NVI weakens too. The combination is what Fosback used as a confirmed bear-market reading.

How can investors use the positive volume index PVI effectively? Plot it with its 255-day SMA, focus on the downside cross as the strongest signal, and combine with breadth and trend tools. Use it as confirmation, not for short-term entries.

How is the positive volume index PVI different from the negative volume index? PVI updates only on higher-volume days and is read as a crowd-flow proxy. NVI updates only on lower-volume days and is read as a smart-money proxy. The two are used together for regime calls.

Sources

1. Fidelity Learning Center, Positive Volume Index. https://www.fidelity.com/learning-center/trading-investing/technical-analysis/technical-indicator-guide/positive-volume-index
2. Fosback, N. G. (1976). Stock Market Logic. The Institute for Econometric Research. https://archive.org/details/stockmarketlogic0000fosb
3. TradingView Solutions, Positive Volume Index (PVI). https://www.tradingview.com/support/solutions/43000773006-positive-volume-index-pvi/
4. Incredible Charts, Positive Volume Index (PVI). https://www.incrediblecharts.com/indicators/positive_volume_index.php

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.