Variance:
The average of the squared differences from the Mean.
To calculate the Variance, take each difference, square it, and then average the result:
So the Variance is 21,704
And the Standard Deviation is just the square root of Variance, so:
Standard Deviation | |
σ | = √21,704 |
= 147.32… | |
= 147 (to the nearest mm) |
So, using the Standard Deviation we have a “standard” way of knowing what is normal, and what is extra large or extra small.
Rottweilers are tall dogs. And Dachshunds are a bit short … but don’t tell them!
But … there is a small change with Sample Data
Our example has been for a Population (the 5 dogs are the only dogs we are interested in).
But if the data is a Sample (a selection taken from a bigger Population), then the calculation changes!