Choosing a Market Index for Stock Beta Analysis
Summary
The document explains that a stock can belong to several indexes and that the appropriate benchmark depends on the purpose of the beta analysis. To reproduce figures from popular finance websites, it recommends matching their usual benchmark choices, such as a major national index. For consistent comparisons across stocks in one country, it suggests using a broad market index or an investable-market index family.
When the aim is to isolate the risk of holding a particular stock rather than an index, an industry index may be a better benchmark. The choice should reflect the analysis objective, not simply the stock’s membership list. The response also stresses using historical total returns that include dividends when regressing against an index. It offers practical selection principles but no empirical comparison showing which benchmark performs best; the choice remains dependent on the intended interpretation of beta.
Key ideas
- Choose a benchmark according to the purpose of the beta calculation.
- To reproduce published beta figures, use the benchmark favored by the source being matched.
- A broad national index can provide a consistent benchmark for stocks in one country.
- An industry index may help measure stock-specific risk relative to its sector.
- Use historical total returns, including dividends, for index regressions.
Tags
Full text
# How do you find the corresponding market index of a stock? # How do you find the corresponding market index of a stock? If I have a stock, we say MSFT, and I want to find its corresponding market index - how do I do this? I thought I needed to start by finding out which index the stock, in this case MSFT, is included in and from there I know which is its market index. However, I have discovered that it is very difficult to find a answer to which index a certain stock belongs to and it also seems that some belong to several indices. So, how do you really find the corresponding market index of a stock? And if it belongs to several indices, which one should I use if I want to check the market index for a specific stock? As an example, here I found a list of which index memberships MSFT belongs to. But if I want to analyze MSFT corresponding market index - which one should I download data from? ## Answer by Dimitri Vulis (score 4) https://quant.stackexchange.com/a/71237 Generally, it depends on what you want to do with tbe index beta. If you want to match the betas on popular web sites like Yahoo Finance, then for all U.S. stocks you'd use S&P 500 (even for stocks that are not S&P 500 constituents), for France you'd use CAC 40, for Germany you'd use DAX, etc - just match the choices of whomever you're trying to replicate. If you don't care about matching other calculations, but you do want to use the same index for all the stocks in one country, then use the broadest index, e.g. Russell 3000 in the U.S. Or look at MSCI's Investable Markets Indexes family. If you are not constrained to use one index per country, but your objective is to minimize the incremental risk shown to be due to holding a specific stock rather than an index, which is a common application of CAPM beta, then choose an industry index (such as semiconductors or financials). But be sure you can find the historical total returns (cum dividends) not just price returns for indexes you choose to regress against.
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