The median size of their principal homes was a little over 5,600 square feet. Some were far bigger. A key finding was that stock performance tended to deteriorate after a CEO bought or built an extremely large or costly estate, which the researchers defined as over 10,000 square feet or sited on more than 10 acres. On average, these companies’ stocks underperformed the S&P 500 index by about 25 percentage points over the three years after the purchase.