Standard Deviation, Variance, and Range

Knowing how disperse your data are fundamental for good quantitative work and it is often presented alongside a measure of centre.  

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Resource: Variance and standard deviation (Statistics Canada)
Type: Article 
Who it’s for: Anyone looking for an explanation of variance and standard deviation that is presented in words. If mathematical notation is not your forte, this resource may be for you. 
Why we love it: This article presents not just how to calculate variance and standard deviation but extends into explaining how to interpret them, using practical examples. Several helpful rules of thumb are also provided. 

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Resource: Dispersion: Variance and Standard Deviation (Introduction to Applied Statistics for Psychology Students – University of Saskatchewan Open Press) 
Type: Textbook chapter 
Who it’s for: Learners who are comfortable with mathematical notation and who are familiar with the difference between samples and populations 
Why we love it: This is a more advanced resource that will get you up to speed on standard deviation and variance while being mindful of the differences between population parameters and sample statistics.