When I wrote about computing stock betas in 2010, I had no idea it would be this blog’s third most popular topic. I wrote a handful of blog posts about stock beta, but my heart wasn’t in them. Today, driving home from the airport, I was inspired to blog about beta for perhaps the last time. Previously I held back and focused on the mechanics of beta computation, and the discrepancies I was seeing between various website’s beta values. This time I provide an example beta-computation spreadsheet and don’t hold back on the math or the theory. Before I launch into this final word on beta, here a few highlights.

- Beta is easy to find online. Not all sites agreed on value, but the delta seems less than it was 2 years ago. Why compute beta when you can simple look it up?
- Beta is less useful if it has a low R-squared. Luckily, sites like Yahoo! Finance provide R-squared values.
- Even with a high R-squared, beta is not a very useful risk measure. Standard deviation is better in many ways.
- In theory high-beta stocks (>3) should go up dramatically when the market goes up. In practice this is often not the case.
- In theory low-beta stocks (<0.5) should be “safer” than the market. Again not so true.
- In theory low-beta stocks (<0.5) should “under-perform.” Not necessarily.

If you are still interested in beta, simply click to read the full-beta blog.