The yield that the investment itself has achieved if all distributions were taken in cash, and not re-invested back into the investment. This yield is independent of when you invested. The formula for calculating the distributed fund yield is:
where the yield is 'i', and where each term is between the ending date of the yield term (the date the yield is being calculated 'to') and the date of the particular transaction. The variables distx represent distributions. The Ending share price is the closing price of the investment on the ending date of the yield term. The Starting share price is the opening price of the investment on the beginning date of the yield term. (This opening price is the same as the closing price of the previous day.)
Annualizing:
By default, yields for terms less than one year are not annualized, and yields for terms greater than one year are average annualized. Whether or not to average annualize yields can be controlled from the Preferences - Yield dialog.
Fund Performance - Reinvested Distributions