Definition of Standard Deviation



Standard deviation is a measure about how much a number or a value is deviating from the mean of the whole data set. In other words, it tells us how much is data scattered. The formula for calculating the standard deviation is as follows:

Standard Deviation Formula

 


Example of Standard Deviation:

Assume that in a class 10 students have scored the following marks in math test: 25, 35, 65, 75, 64, 43, 59, 71, 91 and 32. To calculate the standard deviation, first, calculate the mean.

Mean Calculation of Standard Deviation

 


Then we have to take the squares of the difference between mean and each student’ score.

Scores

Mean

Mean - Score

 (Mean - Score)2

25

56

31

961

35

56

21

441

65

56

-9

81

75

56

-19

361

64

56

-8

64

43

56

13

169

59

56

-3

9

71

56

-15

225

91

56

-35

1225

32

56

24

576

 

 

 

4112

 


Using the above formula the standard deviation will be as follows:

Standard Deviation Calculation Results

 

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