What Apples-To-Apples Market Breadth Is Telling Us

 | May 24, 2015 12:23AM ET

In light of the recent weakness of the Dow Jones Transports, there has been a greater focus on the idea of market breadth and what it tells us. I have heard a lot about how the Transports don`t represent the US economy or market in the same way when Charles Dow first devised the Dow Theory. When you boil it all down, the divergence between the DJIA and DJTA represents a form of breadth divergence.

The best representation of market breadth can be explained this way. When an army is advancing, you want to know if only the generals are leading the charge or if the whole army is moving forward. In market terms, the generals represent the heavyweights of the market, while the army represent the broader market. A market rally on positive breadth is said to be supported by the broad market. By contrast, a rally on narrow breadth is led only by the leadership of the heavyweights and such advances are interpreted with greater skepticism.

In the past, common breadth measures have included the NYSE Advance-Decline Line or NYSE Composite. In more modern times, one problem with this approach is that the underlying components of NYSE-listed stocks do not include the more growth oriented NASDAQ stocks. In addition, the NYSE Composite has a number of closed-end funds and REITs which may not be representative of the broad market (aka the army).

h3 An apples-to-apples breadth metric/h3

What is needed is an apples-to-apples comparison of market breadth.

Enter the S&P 500 A-D line and Equal weighted SP 500 as a breadth benchmark for the SPX. These measures do not suffer from the shortfalls of the NYSE A-D Line or NYSE Composite because they measure the breadth of the same stock universe.

Each is slightly different. The A-D Line is a diffusion index. A single stock advancing will have the same impact on the A-D Line regardless of whether the magnitude of the advance is 0.1% or 10%. By contrast, a 0.1% advance in a stock will affect the Equal-weighted SP 500 differently than a 10% advance. The difference between the equal-weighted and float-weighted SP 500 is that the movements in heavyweights such as Apple (NASDAQ:AAPL) will affect the float-weighted index far more than the smallest stocks in the index.

The chart below shows the 10-year record of the SP 500 and the A-D Line and Equal-weighted SP 500. In order to graphically exaggerate divergences, I have graphed the ratios of the A-D Line to the SP 500 (in green) and Equal-weighted SP 500 to the float weighted SP 500 (in red).