The first step in calculating the standard deviation is to calculate the mean, x. In this case, x = 10.

Now, subtract that mean from each of the data values, and then square those results:

Table VII
Urea Nitrogen Concentration in 5 Employees (mg/dL)

Concentration (mg/dL)	x-	(x-)2
9	-1	1
7	-3	9
11	1	1
13	3	9
10	0	0
Total		20

Use this total to calculate the standard deviation:



The standard deviation is about 2.23.