Oh, that makes sense. Do you have any reference for it? I found this explanation http://www.investopedia.com/ask/answers/040215/what-does-sp-500-index-measure-a

Oh, that makes sense. Do you have any reference for it? I found this explanation http://www.investopedia.com/ask/answers/040215/what-does-sp-500-index-measure-and-how-it-calculated.asp http://www.investopedia.com/ask/answers/040215/what-does-sp-..., but it doesn't seem all that trustworthy, and it seems to suggest that S&P doesn't account for survivor bias.