Key Points The S&P 500 is historically expensive. The last time the S&P 500 was this expensive was during the dot-com bubble. 10 stocks we like better than S&P 500 Index › The Shiller price-to-earnings (P/E) ratio, or CAPE ratio, is a measure of how expensive the S&P 500 (SNPINDEX: ^GSPC) is. At the time of this writing, the Shiller P/E ratio is just over 40 -- a mark it has hit only once before -- in the thick of the dot-com bubble. Unfortunately, we know how the dot-com bubble played out, with t ...