COMPUTATION OF THE RATE OF INTEREST
The formula for the computation of the rate of interest for the reference year is the following:
iy = ((1+ Ty-1) (1 + Ty-2) (1 + Ty-3)) 1/3 - 1
where
Ty-1 is the rate of return for the year preceding the reference year
Ty-2 is the rate of return for the year occurring 2 years before the reference year
Ty-3 is the rate of return for the year occurring 3 years before the reference year.