We estimate the gross monthly return on each common stock investment using the beginning-of-month position statements from our household data and the CRSP monthly returns file. In so doing, we make two simplifying assumptions. First, we assume that all securities are bought or sold on the last day of the month. Thus, we ignore the returns earned on stocks purchased from the purchase date to the end of the month and include the returns earned on stocks sold from the sale date to the end of the month.
Second, we ignore intramonth trading ~e.g., a purchase on March 6 and a sale of the same security on March 20!, though we do include in our analysis short-term trades that yield a position at the end of a calendar month.