:
no.of issues deviation from square of dev. percentage
seen average
0 -1 1 50
1 0 0 20
2 1 1 15
3 2 4 10
4 3 9 5
The average square deviation is
(50x1 + 20x0 + 15x1 + 10x4 + 5x9)/100 =
= (50+15+40+45)/100
= 150/100
= 1.5
So the SD is equal to the square root of 1.5