Calculate: Standard Deviation

November 5, 2008 by  
Filed under Dispersion, How To Calculate

Regardless of how you obtained variance (by dividing by N or by N-1), you calculate the standard deviation by taking the square root of variance.

Take what you calculated variance to be. Put it in your calculator and push this button:

 

The result is the standard deviation.

NOW YOU CHOOSE:
Day 3: Dispersion
A Bit More About Dispersion
Even More About Dispersion
Range
MAD
Sum of Squares
Variance
Standard Deviation
How To Calculate
Range
MAD
Sum of Squares
Variance
Standard Deviation
Formulas For Dispersion
Practice Problems
More Practice Problems
Basic Facts About Dispersion
Vocabulary
Quiz 3
Summary

 

Calculate: Variance

November 5, 2008 by  
Filed under Dispersion, How To Calculate

The fourth measure of dispersion is variance. Variance is the Sum of Squares divided by N

Variance of a population is always SS divided by N; regardless whether it is a large population or a small population.

Variance of a large sample (where N is equal to or larger than 30) is calculated like a population. Divide SS by N.

If the sample is small (less than 30), adjust for the small sample size by dividing SS by N-1.

 

NOW YOU CHOOSE:
Day 3: Dispersion
A Bit More About Dispersion
Even More About Dispersion
Range
MAD
Sum of Squares
Variance
Standard Deviation
How To Calculate
Range
MAD
Sum of Squares
Variance
Standard Deviation
Formulas For Dispersion
Practice Problems
More Practice Problems
Basic Facts About Dispersion
Vocabulary
Quiz 3
Summary

Calculate: MAD

November 5, 2008 by  
Filed under Dispersion, How To Calculate

Mean Absolute Deviations (MAD) is a measure of dispersion.
Start by subtracting the mean from each score. Put the answers in a colum labeled d (use little d because these are deviations).
Take the absolute value of the d’s. Ignore the sign (positive or negative), and add up the magnitudes.