Standard deviation (SD)
Standard deviation is the square root of the mean of the squared deviations of the individual observations from the mean. Of all the different measures of dispersion, standard deviation is the most important one and is mostly used in various statistical methodologies.
Calculation of standard deviation: The pulse rates per minute of 10 students in a class are as follows:
80, 90, 96, 80, 94, 72, 84, 92, 82, 90.
The standard deviation of the pulse rate for the group is calculated as follows:
Mean = (80+ 90+ ……+ 82+ 90)/10 = 860/10 = 86.
x1 x1 – x̅ (x1 – x̅)2
80 80-86 36
90 90-86 16
96 96-86 100
80 80-86 36
94 94-86 64
72 72-86 196 SD= root of (x1– x̅)2/n
root of 520/10= 7.21 per min.
84 84-86 4
92 92-86 36
82 82-86 16
90 90-86 16
——
520
