The Market-Top Breadth Deterioration Model
Detect market tops by watching participation erode beneath headline indexes
- Difficulty
- Advanced
- Time to result
- ~months to results
- Steps
- 5
- Confidence
- 99%
This model rejects the idea that the stock market moves as a single unit near major peaks. Desmond argues that tops develop through progressive internal deterioration: speculative small-cap stocks weaken first, mid-cap stocks follow, and large-cap leaders turn last. Because capitalization-weighted indexes emphasize the largest companies, those indexes can remain near records while a substantial share of the market is already declining or in individual bear markets. Investors therefore inspect participation directly through new-high statistics, drawdowns, segmented breadth, and the advance-decline line. As fewer stocks support the advance, portfolios should shed deteriorating holdings and become more defensive before weakness finally becomes visible in headline indexes.
Origin
Lowry's reconstructed historical market data, including records surrounding the 1929 peak, to study how individual stocks behave before major bear markets. Extracted from Masters in Business.
Core principles
- 01Markets usually fragment before major tops
- 02Small-cap weakness tends to precede mid-cap and large-cap weakness
- 03Capitalization-weighted indexes can conceal widespread deterioration
- 04Falling participation is an early warning, not background noise
- 05Analyze individual stocks and market segments rather than treating the market as one entity
How to run it
- 1
Divide the market by capitalization
Analyze small-, mid-, and large-cap stocks separately. This prevents large companies from masking weakness in more numerous smaller issues.
Pro tip Use equal-weighted or issue-level data alongside capitalization-weighted indexes.
Watch out A headline index can look healthy even while most listed stocks are weakening.
- 2
Measure participation
Track the proportion of stocks making new highs and the proportion already materially below their own highs. Healthy advances should involve broad participation.
Pro tip Compare current participation with the much broader new-high participation normally seen early in bull markets.
Watch out A new index record is not equivalent to a new high for the typical stock.
- 3
Track the deterioration sequence
Look for sustained weakness beginning in small caps, spreading into mid caps, and eventually reaching large caps. Treat that progression as evidence that the bull market is aging.
Pro tip Record when each segment peaks rather than assigning one peak date to the entire market.
Watch out Segments can temporarily diverge for reasons unrelated to a major market top.
- 4
Confirm with cumulative breadth
Monitor the advance-decline line to determine whether more stocks are consistently falling than rising. A persistent divergence from a rising headline index strengthens the warning.
Pro tip Focus on multi-month deterioration rather than isolated weak sessions.
Watch out Breadth indicators built from mixed security types may be distorted.
- 5
Cull and defend
Remove stocks that have already dropped out of the uptrend and reduce aggregate risk as deterioration spreads. The objective is to prepare before large-cap indexes finally break.
Pro tip Treat portfolio-level deterioration as actionable even if financial media still describes the market as strong.
Watch out Do not rely on one breadth statistic without checking the underlying security universe.
In the wild
When the Dow Jones Industrial Average reached its September 1929 peak, Desmond's reconstructed data showed that only 2.3 percent of New York Stock Exchange stocks were making new highs. Roughly 35 percent were already down materially from their own highs, while the advance-decline line had been falling for about two years.
→ The internal market warned of deterioration long before the headline average made the danger obvious.
At the October 2007 market top, only eighteen stocks in the S&P 500 were making new highs. The capitalization-weighted index obscured the fact that participation had narrowed to a small fraction of its constituents.
→ New-high breadth exposed fragility beneath the index before the financial-crisis bear market.
Common mistakes
Treating the index as the market
A capitalization-weighted index mainly reflects its largest members and can conceal weakness across hundreds or thousands of other stocks.
Ignoring small-cap weakness
Small stocks may appear unimportant individually, but collectively they can provide the earliest evidence that risk appetite is deteriorating.
Using a contaminated breadth universe
Breadth calculated across bonds, preferred shares, funds, and operating companies can blur the behavior of domestic common stocks.
Is it for you?
Best for
It is best for portfolio managers and investors monitoring mature bull markets for evidence of narrowing participation.
Not ideal for
It is not ideal as a precise short-term entry or exit trigger when used without price, volume, and momentum confirmation.
From the transcript
“individual stocks drop out of the bull market one by one by one, very much like the leaves falling off the trees.”
“The process starts with the small caps. Almost always starts with the small caps. Then it moves to the mid caps.”
“because the big caps are the last thing to turn down.”
From the episode
An Interview With Paul Desmond: Masters in Business (Audio)
Paul Desmond