VARIANCE

Variance

The Variance is defined as:
The average of the squared differences from the Mean.
To calculate the variance follow these steps:

  • Work out the Mean (the simple average of the numbers)
  • Then for each number: subtract the Mean and square the result (the squared difference).
  • Then work out the average of those squared differences. 

Example

You and your friends have just measured the heights of your dogs (in millimeters):
The heights (at the shoulders) are: 600mm, 470mm, 170mm, 430mm and 300mm.
Find out the Mean, the Variance, and the Standard Deviation.
Your first step is to find the Mean:

Answer:

Mean =  
600 + 470 + 170 + 430 + 300
  =  
1970
  = 394
5
5
so the mean (average) height is 394 mm. Let's plot this on the chart:
Now, we calculate each dogs difference from the Mean:
To calculate the Variance, take each difference, square it, and then average the result:
So, the Variance is 21,704.
S-BATCH