How to write the formula of Sum of Squared Deviation with SD and n in R?

Question

mathematical formula to calculate standard deviation is $SD = (\frac{SSD}{n-1})^{0.5}$

Would like to find SSD and how to write in r ?

SSD = ????

@ralph thanks ralph! but can you show the working to convert that to sd^2? — Learner, Jun 05 '21 at 11:06
Square both sides (to remove the square root), then multiply both sides by $(n - 1)$. — ralph, Jun 05 '21 at 11:09

score 3 · Answer 1 · answered Jun 05 '21 at 11:13

3

I'll use $\sigma$ for SD to avoid confusion with SSD:

If $\sigma = (\frac{SSD}{n-1})^{0.5}$, then

$\sigma^2 = \frac{SSD}{n-1}$. Therefore:

$SSD = \sigma^2 (n-1)$

answered Jun 05 '21 at 11:13

David

2

So sd(x)^2 * (length(x) - 1) in R (or var(x) * (length(x) - 1)) – Dave Jun 05 '21 at 12:05

1 Answers1