The twosided confidence interval for the mean has upper and lower limits

where and is the percentile of the distribution with degrees of freedom. The onesided upper confidence limit is computed as and the onesided lower confidence limit is computed as . See Example 4.9.
The twosided confidence interval for the standard deviation has lower and upper limits,

respectively, where and are the and percentiles of the chisquare distribution with degrees of freedom. A onesided confidence limit has lower and upper limits,

respectively. The confidence interval for the variance has upper and lower limits equal to the squares of the corresponding upper and lower limits for the standard deviation. When you use the WEIGHT statement and specify VARDEF=DF in the PROC statement, the confidence interval for the weighted mean is

where is the weighted mean, is the weighted standard deviation, is the weight for th observation, and is the percentile for the distribution with degrees of freedom.