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The Standard Deviation

 
Variability Quiz
The Standard Deviation Home Introduction to the Standard Deviation Why do you need a measure of Variability? Measuring the Average Distance to the Mean Variability Quiz Population versus Sample Standard Deviation Standard Deviation Calculation Standard Deviation Calculation Short-Cut Method The Standard Deviation with Excel and The Online Calculator Standard Deviation in Practice Standard Deviation QuizView All Tutorials
 Standard Deviation Calculation
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Things to remember:
  1. σ is the population standard deviation which we usually don't know.
  2. s is the sample standard deviation which is an estimate of the unknown population standard deviation.
  3. We divide the sum of squares by 1 less than the sample size to account for the error in estimation from the sample standard deviation (called the degrees of freedom).

 
Variability Quiz
The Standard Deviation Home Introduction to the Standard Deviation Why do you need a measure of Variability? Measuring the Average Distance to the Mean Variability Quiz Population versus Sample Standard Deviation Standard Deviation Calculation Standard Deviation Calculation Short-Cut Method The Standard Deviation with Excel and The Online Calculator Standard Deviation in Practice Standard Deviation QuizView All Tutorials
 Standard Deviation Calculation

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March 15, 2009 | Anthoyn wrote:
sample standard deviation (called the degrees of freedom). the df n-1 should be earlier in the sentence otherwise it reads sort of like the sample standard deviation(ALSO called the degrees of freedom
 
February 17, 2009 | Rodrigo Averna wrote:
Why did we didvide the sum of sqared values by " one less than the sample size" and not the sample size?