I don't get why the sum of yearly returns/risk is not the exact sum of the months. I mean, for example, STV in 2015 has a total return of 29.48%, but if I sum all the months in that year, the number I get is 26.87%.
Also, it has a total % return of 207.65%. But If I sum the total of every year the result is very different (39.23+29.48+32.93+16.65+10.06 == 128.44%)
Why does this happen? Is it because the win/loses are compounded?