TECHNOLOGY OVERVIEW

Confidence Intervals for the ratio of two standard deviations of a Normal Variate

BIS.Net Team

The mainstream confidence interval limits are normally set at

LL=sqrt(Sd1^2/(Sd2^2*F(n1-1,n2-1,alpha1)))

UL= sqrt((Sd1^2/(Sd2^2))*F(n2-1,n1-1,alpha2)))

Where:

Sd1 is the sample standard deviation for population 1

Sd2 is the sample standard deviation for population 2

n1 is the sample size for population 1

n2 is the sample size for population 2

alpha1+alpha2 = level of significance alpha. The Confidence Coefficient is equal to 1-alpha1-alpha2. The % Confidence Coefficient is equal to 100* (1-alpha1-alpha2)

F is the F variate for the specified degrees of freedom and probability.

Alpha1 and alpha2 are found using a machine powered algorithm to obtain the smallest possible interval whilst ensuring that the specified confidence coefficient is met.