Negative Returns on Addition to the S&P 500 Index and Positive Returns on Deletion? New Evidence on the Attractiveness of S&P 500 vs. S&P 400 Indexes

Abstract

In recent years, the majority of additions to and deletions from the S&P 500 index have been stocks that were previously or subsequently included in the S&P 400 index. The announcement returns of these changes have been the opposite of what has been documented for all S&P 500 additions and deletions in an extensive literature. During 2016-2019, such ‘upward additions’ to the S&P 500 index resulted in an average announcement excess return of -2.31% over a three-day period while ‘downward deletions’ resulted in an excess return of +1.21%. We explain these new results by the increasing ownership of S&P 400 stocks by institutional investors, the majority of whom are active fund managers. Our results thus show the increasing benefits of being included in the mid-cap S&P 400 index relative to being included in the large-cap S&P 500 index.