The S&P 500 is top-heavy, but so are fundamentals

There has been much discussion about the increasing concentration of the market cap weighted indices in the US, with the S&P 500 now showing some of the highest levels of concentration among the largest constituents in history. The top 20 S&P 500 stocks (4% of the constituents) currently comprise 38.6% of the index weight, while the top five companies alone make up 23.8% of the weight.