I discuss confidence intervals for a single population variance. The methods used here are based on the assumption of sampling from a normally distributed population (these methods involve the chi-square distribution). The underlying logic behind the form of the interval is discussed, and an example is then worked through.
N.B. There is a typo at 0:36, where the square is missing on the sample variance formula. The sample variance is of course the sum of squared deviations from the sample mean, divided by n-1.