Determination of the Confidence Interval of the Relative Standard Deviation Using Convolution
- 769 Downloads
Coefficient of variation is a widely used measure of dispersion and is important in comparing variables with different units or average values. In pharmaceutical industry, it is termed as the relative standard deviation (RSD) and is used widely to describe blend concentration variability, finished dose variability, dissolution q point variability, etc. Although theoretical formula and simulation methods for the estimation of the RSD confidence interval have been developed in previous literature, they are not well known, and they are either too complex to apply easily or require intensive computation. As a result, the statistical reliability of RSD estimates are rarely evaluated, which increases process risk as well as consumer risk. In this paper, we introduce a novel convolution numerical method for the quick and straightforward estimation of RSD confidence intervals. A standard statistical distribution group is developed, denoted as the Chi-on-Mu-square distribution, which is similar to the widely used Chi-square distribution. Results indicate the Chi-square distribution itself can be a good approximation in the RSD confidence interval calculation, especially when small RSD is expected or large number of samples is involved. The effect of deviations from the normal distribution populations is also discussed.
KeywordsCoefficient of variation Confidence interval Relative standard deviation Quality by design
This work is supported by the National Science Foundation Engineering Research Center on Structured Organic Particulate Systems, through grant NSF-ECC 0540855 and by grant NSF-0504497.
- 3.Food and Drug Administration. Guidance for industry: powder blends and finished dosage units—stratified in-process dosage unit sampling and assessment. In: Gad SC, editor. Pharmaceutical Manufacturing Handbook: Regulations and Quality. Hoboken: Wiley; 2003Google Scholar
- 9.Almonte C, Kibria BMG. On some classical, bootstrap and transformation confidence intervals for estimating the mean of an asymmetrical population. Model Assist Stat Appl. 2009;4(2):91–104.Google Scholar