Confidence Intervals

By default, the SURVEYPHREG procedure computes t confidence limits for the estimated regression coefficients. Alternatively, you can specify the DF=NONE option in the MODEL statement to request standard normal confidence intervals. The t confidence interval for a linear combination of the regression coefficients is computed as

where is the percentile point of the distribution with degrees of freedom. See the section Degrees of Freedom for more information about . If you use the DF=NONE option in the MODEL statement, then the procedure uses the percentile point of the standard normal distribution.