Stock Price Charts

which index does yahoo finance and google finance use to calculate a stock price's beta?

I know what beta is see here - http://www.investorguide.com/igu-article-823-stock-basics-measuring-a-stocks-risk.html What I want to know is why: Google Finance calculates YHOO Beta as 1.74 while Yahoo finance calculates YHOO Beta as as .44 How do I find out the R-square and which stock index these portals are using to calculate beta, i.e. SP500? etc. etc. Thanks guys! so i guess to phrase the question differently....how do i calculate the Beta for my own personal portfolio . . .?

Public Comments

1. They're probably using different time periods to calculate the beta. To calculate beta you have to use regression analysis with a calculator or Excel.
2. The "Gummy Stuff" website can be an interesting source of calculating such things. Take a look at: http://www.gummy-stuff.org/beta.htm There is a spreadsheet you can download from that page. As far as your original question -- you have to go to their help pages and glossaries to find the definitions of their data items. Last time I looked: IBD defined theirs as a 12-month calculation Yahoo defined theirs as a 3-year calculation Zacks and Reuters defined theirs as a 5-year calculation Since Google generally gets their data from Reuters, I would suspect their beta is also based on a 5-year calculation.
3. YHOO Beta isn't .44, so something is incorrect. It is probably tracking the S&P 500, although that doesn't matter too much. The only main discrepancy could be how many years back they are doing the correlation. FT has r sqaures, I think?