Over the past 20 years, a trend toward index fund investing has emerged. Currently, more mutual fund assets are indexed to the S&P 500 than any other index. Prior research on downward-sloping demand curves suggests that widespread acceptance of S&P 500 index investing may push prices of...

While major stock market indices are followed by large monetary investments, we document that membership decisions for the S&P 500 index have a nontrivial amount of discretion. We show that firms' purchases of S&P ratings appear to improve their chance of entering the index (but purchases of...