As market participants, we should be taking a scientific approach when putting money to work, always assuming our positions are wrong and need to prove themselves. As part of that process, one piece of evidence we want to look at on a consistent basis is the health of the overall market.
One such way to gauge market health is studying market breadth. In other words, how many stocks are actually participating in any directional move. That’s why we’re writing today about an index you might not be aware of but should be familiar with if you follow our research. This index is great at providing insight into the current condition of the U.S. stock market: the Value Line Geometric Index (XVG). This index tracks the median move of stocks within the index using the assumption that each stock has an equal amount (for example, $1,000) invested in them. The daily average move of this index is calculated geometrically (rather than arithmetically). If you want to geek out on the details, you can read more about this calculation here, page 4.
In basic terms, the Value Line Geometric Index eliminates an illusion created by cap-weighted index components. Heavily weighted stocks within a cap-weighted index can pull it higher even as the majority of the stocks within the index are not following along. For example, in a cap-weighted index like the S&P 500, it’s possible for the top 100 weighted stocks to carry the index higher while the remaining 400 stocks lose value. As an investor, it might be helpful to identify when this is happening.
The last time we wrote about this Index, we noted it needed to hold and advance beyond the $500 level. Here’s the chart of the Value Line Geometric and S&P 500 Indexes from that post.
(Click on image to enlarge)
Here’s an updated chart comparing the popular cap-weighted S&P 500 Index with the lesser-known Value Line Geometric Index:
(Click on image to enlarge)
