I am researching the past five year return for the securities in the top and bottom 10 percentile of the S&P 500 on date 5 years ago. I used Bloomberg to get this data. When I searched for the top 10 percent of stocks based on P/E ratio in the S&P 500 5 years ago, my searched returned 48 stocks. Why was it 48 instead of 50?
This is possible for many reasons; one of which was explained by John. Another reason could be what you used for your P/E multiple. If it was a direct field providing you the ratio, then there is a possibility that a couple of those stocks had a negative EPS that period. Bloomberg (and many similar data vendors) do not calculate a ratio if the denominator is negative. A workaround to this is to have the P/E calculated yourself by looking at Price and EPS individually.