Finding the combined standard deviation
Suppose i have 2 sets
Set A: number of items = 10, mean = 2.4 , S.D = 0.8
Set B: number of items = 5, mean = 2, S.D = 1.2
Ok i can find the combined mean easily, but how am i supposed to find the combined standard deviation?
Any help would be greatly appreciated...
Re: Finding the combined standard deviation
1. Var(A+B) = Var(A) + Var(B) ( Given that both observations are independent; Otherwise, Var(A+B) =/= Var(A) + Var(B) )
2. 1.2 square + 0.8 square = 2.08 (this is the combined variance)
3. square root 2.08 = 1.442 (combined standard deviation)