Quality and Reliability Methods - SAS

388 Reliability and Survival Analysis II Chapter 20
Proportional Hazards Model
Figure 20.16 Fit Model Dialog for Proportional Hazard Analysis
Statistical Reports for the Proportional Hazard Model
Finding parameter estimates for a proportional hazards model is an iterative procedure. When the fitting is
complete, the report in Figure 20.17 appears. The Iteration History table lists iteration results occurring
during the model calculations.
• The Whole Model table shows the negative of the natural log of the likelihood function
(–LogLikelihood) for the model with and without the grouping covariate. Twice the positive difference
between them gives a chi-square test of the hypothesis that there is no difference in survival time
between the groups. The degrees of freedom (DF) are equal to the change in the number of parameters
between the full and reduced models.
• The Parameter Estimates table gives the parameter estimate for Group, its standard error, and 95%
upper and lower confidence limits. For the Rats.jmp sample data, there are only two levels in Group;
therefore, a confidence interval that does not include zero indicates an alpha-level significant difference
between groups.
• The Effect Likelihood-Ratio Tests shows the likelihood-ratio chi-square test on the null hypothesis that
the parameter estimate for the Group covariate is zero. Group has only two values; therefore, the test of
the null hypothesis for no difference between the groups shown in the Whole Model Test table is the
same as the null hypothesis that the regression coefficient for Group is zero.