Page 82 - Radiation Safety

STATISTICAL CALCULATIONS

Standard deviation

• The standard deviation is a measure of the dispersion of a set of values.

• The standard deviation is usually denoted with the letter σ.

• Example 3, 7, 7, 19

1  N  _  2 
 =   x − x  
N  i  i  

 =1

find mean, x = (3+7+7+19) /4 = 9

find deviation of each number from the mean

3-9 = -6, 7-9 = -2, 7-9 = -2, 19-9 = 10

square each of the deviations

2
2
2
2
(-6) , (-2) , (-2) , (10) = 144
divide the sum 4
144/4 = 36

Take the non-negative square root

therefore, σ = 36 = 6