New Home Edition User Confused by Variance result.

Questions
,
1

Calculate the Mean and StandardDeviation of a list: 140,120,100,80,60. Okay the answers should be - mean = 100, standard deviation = 28.28, variance = 800. I can’t understand why Mathematica says the standard deviation is 31.6228 and the variance is 1000. The formula for variance in the documentation is the same as my spreadsheet formula, I can’t understand why the result is different. Please help out a new user and tell me where I am going wrong.

list1={140,120,100,80,60}

Mean[list1]

N[StandardDeviation[list1]]

N[Variance[list1]]
2

In this case, 800 is the biased sample variance. As documented, the function Variance uses Bessel’s correction and returns the unbiased sample variance, 1000.

3

Thank you for your reply. Okay, the number of observations used to figure the variance is N-1. I feel funny about not seeing that before, like not realizing my t-shirt is on backwards.