# MandysNotes

## Standard Deviation (6)

Sunday, 12 February 2012 22:57

### Standard Deviations and Cuttlefish

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Question:

What's the difference between sample standard deviation and population standard deviation? When do we use N-1 and when N in the denominator?

Saturday, 23 January 2010 00:00

### Sample Standard Deviation

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The sample standard deviation is almost the same formula as Lowercase Sigma = Population Standard Deviation, except that the denominator calls for N - 1 (one less than the number of values given).

Friday, 22 January 2010 19:23

### Mean & Standard Deviation

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Disclaimer: I did not create nor do I own these videos. I have simply embedded them, courtesy of YouTube.

Notice this:

The SAMPLE MEAN and the POPULATION MEAN are found using exactly the same formula.

The ONLY difference between the two is that the SAMPLE MEAN is referred to as "x bar" whereas the POPULATION MEAN is referred to as "mew."  BOTH are found by calculating the SUM of all values you are given and dividing by "N," the number of values you are given.

Friday, 22 January 2010 19:18

### Calculating the VARIANCE

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"Variance" seems like a term unrelated to standard deviation, but in fact - the variance is just the SD^2 (Standard Deviation, Squared).

The reverse is therefore true.  The Standard Deviation is the SQUARE ROOT of the variance.

;

Friday, 22 January 2010 18:44

### Interpreting the Standard Deviation

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Disclaimer: I did not create nor do I own these videos. I have simply embedded them, courtesy of YouTube.

Friday, 22 January 2010 18:41

### Introduction to the Standard Deviation

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Disclaimer: I did not create nor do I own these videos. I have simply embedded them, courtesy of YouTube.

The Standard Deviation is the SQUARE ROOT of the VARIANCE.

The official formula for the POPULATION Standard Deviation is: