# Standard Deviation and Varians

• Mar 31st 2010, 01:23 PM
nursetobe
Standard Deviation and Varians
I first of all apologize if this is the wrong category. This is for a Statics class at college level, but basic statistics.

I am really having a hard time and confusing myself when it comes to the standard deviation and variations. The formulas (do the best I can without the keys needed on the keyboard) are:

O2m = O2 squared / N - this is variance

Om = this is standard deviation (standard deviation / N squared = standard deviation)

When given a problem are we be given one or the other to calcuate and then continue with the rest of the steps. For example if I am given the standard deviation of 8 and my N = 10 then 8/10 = .80 so this would be my standard deviation.

Would I also then calcuate a variance or or is that only if you are given the variance in the problem you would then use the formula to determine your variance.

This is the only part I am having a really hard time grasping. Ugh.

• Mar 31st 2010, 01:59 PM
matheagle
Hello Nurse Toby.

The problem seems to be the terminology
Let $\displaystyle \sigma^2$ be the variance of one observation whether thats $\displaystyle X_1$ or $\displaystyle X_2$....
It's the variance of each one of them.

NOW the sample mean is $\displaystyle \bar X={X_1+...+X_n\over n}$

and the variance of $\displaystyle \bar X$ is $\displaystyle \sigma^2/n$

and the st deviation of $\displaystyle \bar X$ is $\displaystyle \sigma/\sqrt{n}$
• Mar 31st 2010, 02:22 PM
Anonymous1
Quote:

Originally Posted by nursetobe
This is for a Statics class at college level

Statics??? I thought you wanted to be a nurse, not an engineer.

Quote:

Originally Posted by matheagle
Hello Nurse Toby.

(Rofl) hahahaha
• Apr 1st 2010, 05:46 AM
nursetobe