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Standard Deviation
Calculate the mean
Mean = (12 + 8 + 7 + 14 + 4) ÷ 5
x =9
Given a Data Set
12, 8, 7, 14, 4
The standard deviation is a
measure of the mean spread of
the data from the mean.
(25 + 4 + 25 + 1 + 9) ÷ 5 = 12.8
Square root 12.8 = 3.58
25
-5
7
4
n
Calculator 8
function
4
5
6
7
Std Dev = 3.58
4
-2
25
5
1
-1
8
9
3
12
How far is each data
value from the mean?
xx
x  x 
2
 x  x 
2
n
14
9 10 11 12 13 14
x
1st slide
Square to remove
the negatives
Average =
Sum divided by
how many values
 x  x 
2

n
Square root
to ‘undo’ the
squared