On page 84, CFAI vol.5, in exhibit 30 there is an example of how to calcualte a rolling 6m returns mean.
For the mean, in stead of 6 periods, 7 periods are taken for the average calculation.
What is the difference between simply calculating the rolling 6m return (i.e. n=6 periods), vs. a roll return mean i.e. why add the additional period.
I hope anyone can help me with this.