0
$\begingroup$

Hi folks,

I plugged the following set of numbers into Excel:

[600 470 170 430 300]

I found the mean (394), summed the numbers, divided by 5 to get variance (21704). I then did the square root to find stdev (147.32).

Using Excel or Wolfram Alpha's variance and stdev function give me differnt numbers, variance 27130 and stdev 164.71 respectively. Why? I believe I am following the equation as listed on Wikipedia, my stat text book, and the following page:

http://www.mathsisfun.com/data/standard-deviation.html

What am I missing?

Thank you for any help you can give!

$\endgroup$
1

2 Answers 2

0
$\begingroup$

The unbiased variance estimator normalizes by $n-1$, instead of $n$. This may be the difference you're seeing.

$\endgroup$
0
$\begingroup$

You found the population standard deviation; Excel/Wolfram gave the sample standard deviation--the unbiased estimate of the population standard deviation when you have only a sample, not the entire population. Use "stdevp" to get the population standard deviation in Excel.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.