Page 49 - Quality control of pharmaceuticals (07-PA 704)

For small sets of data, the sample standard deviation (S) can be calculated by using
the following equation:

S= √∑ = 1( − ̅ )2

−1

Where Xi – ̅ is the deviation from the mean ( ̅ ) of the measurement.
N= is the number of experiments
Standard deviation value takes the same unit as Xi

2. Variance (S2)
The variance is simple square of the standard deviation:

∑ =1(Xi − ̅ )2
V= S2 = ‫ــــــــــــــــــــــــــــ‬

N-1
The variance has the square unit of that of Xi.

3. Relative standard deviation (RSD)
Sr = S/ ̅

These relative quantities have no units.
When these quantities are multiplied by 102 or 103, they become expressed in
terms of percentage (%) or parts per thousand (ppt), respectively.
Coefficient of variation, CV:
It is the relative standard deviation when expressed as percentage.