Quality and Reliability Methods - SAS

Chapter 19 Reliability and Survival Analysis 361
Univariate Survival Analysis
For the exponential, Weibull, and lognormal Fits, hold down the Shift key, click the red triangle of the
Product-Limit Survival Fit menu, and then click on the desired fit. The following Options window
appears. (In this example, LogNormal Fit was selected.)
Figure 19.13 Options Window
You can set the confidence level for the limits; the constrained value for theta (in the case of an
exponential fit), sigma (in the case of a lognormal fit) or beta (in the case of a Weibull fit); and request a
Confidence Contour Plot for the Weibull and lognormal fits. For details on using constrained values, see
“WeiBayes Analysis” on page 366. An example of a contour plot is shown in Figure 19.14.
Figure 19.14 Confidence Contour Plot
Fitted Distribution Plots is available in conjunction with the fitted distributions to show three plots
corresponding to the fitted distributions: Survival, Density, and Hazard. No plot will appear if you
haven’t done a Fit command. An example is shown in the next section.
Competing Causes prompts for a column in the data table that contains labels for causes of failure.
Then for each cause, the estimation of the Weibull model is performed using that cause to indicate a
failure event and other causes to indicate censoring. The fitted distribution is shown by the dashed line
in the Survival Plot.
Estimate Survival Probability brings up a dialog allowing you to enter up to ten time values. The
survival probabilities are estimated for the entered times.
Estimate Time Quantile brings up a dialog allowing you to enter up to ten survival probabilities. A time
quantile is estimated for each entered probability.