Question: how to calculate confidence interval for variance?
Answer: Confidence Interval Formula [ (n - 1)s2] / B < σ2 < [ (n - 1)s2] / A. Here n is the sample size, s2 is the sample variance. The number A is the point of the chi-square distribution with n -1 degrees of freedom at which exactly α/2 of the area under the curve is to the left of A.