SD – Standard Deviation

Standard Deviation measures the spread around the average. In other words by how much is an element in data away or closer to the average.

What is a Standard Deviation ?

How does one find Standard Deviation ( SD ) ?

SD for any given data can be found in  3 simple steps:

1. Find the Average of data
2. Find its deviation from the Average
3. Find the R.M.S of the deviations

Example sample A: 41, 48 , 50 , 50 , 54 , 57

1. Find the average of sample A . Average = 300/6 = 50
2. Find the deviation of each number in sample A from the Average ( 50 )
   1. 41 – 50 = -9
   2. 48 – 50 = -2 and so on to yield -9, -2 , 0 , 0, 4 ,7
3. Find the Root Mean Square of list in step 2
   1. Square of all values  81 , 4 , 0 , 0, 14 , 49
   2. Average of values in above step 150/6 = 25.
   3. Root of the value got in step 2 , root(25) = 5.

5 is the SD for the sample list 41 , 48, 50, 50, 54, 57.

Standard Deviation is very important while calculating Coefficient of Correlation.Will be discussed in another post !