# Refresh my Memory: Standard Deviation

• June 19th 2011, 05:03 PM
arcketer
Refresh my Memory: Standard Deviation
I vaguely recall a "shortcut" sort of formula for calculating the standard deviation for a population. For example, if theres a yes/no survey and 53% of 1,000 people votes yes, what's the standard deviation from the expectation?

I recall such a formula from my Stats 1 class years ago. It was something like:

(Number voting yes / Total votes) + (Number voting no / Number votes) * sqrt(something)
• June 19th 2011, 05:10 PM
pickslides
Re: Refresh my Memory: Standard Deviation
$\displaystyle \sqrt{np(1-p)}$
• June 19th 2011, 05:13 PM
arcketer
Re: Refresh my Memory: Standard Deviation
Where n is sample size and p is probability of positive respons?
• June 19th 2011, 05:14 PM
pickslides
Re: Refresh my Memory: Standard Deviation
Yep!
• June 19th 2011, 05:16 PM
arcketer
Re: Refresh my Memory: Standard Deviation
Thank you!