Prior to SAS 9.1, the OUTSURV= data set contained linear confidence limits. Beginning in SAS 9.1, the pointwise confidence limits for the survival estimates in the OUTSURV= data set are computed using a log-log transformation. Transformed limits are considered superior to linear confidence limits. A note is written to the SAS log indicating that the log-log transformation is used.

Beginning in SAS 9.1, linear confidence limits are no longer available in the OUTSURV= data set. However, you can obtain transformed confidence limits on the survival function, including linear confidence limits, by specifying the CONFTYPE= option which allows several transformations. The CONFTYPE= option is available in the SURVIVAL statement in SAS 9.1 or the PROC LIFETEST statement beginning in SAS 9.2^NOTE.

For SAS 9.2 or later releases, information on syntax and additional options that can be used can be found in the PROC LIFETEST description in the Syntax section of the PROC LIFETEST documentation. Formulas for the pointwise confidence limits in the OUTSURV= data set can be found in "Computational Formulas: Pointwise Confidence Limits in the OUTSURV= Data Set" in the Details section.

For SAS 9.1, information on syntax and additional options that can be used in the SURVIVAL statement can be found in the SURVIVAL statement description in the Syntax section of the LIFETEST documentation. Formulas for the pointwise confidence limits in the SURVIVAL OUT= data set can be found in "Computational Formulas: Pointwise Confidence Limits Added to the Output Data Set" in the Details section.

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NOTE: Beginning in SAS 9.2, the options in the SURVIVAL statement have been added to the PROC LIFETEST statement and the SURVIVAL statement is obsolete. Also, if you specify the SURVIVAL statement as well as the OUTSURV= option in the PROC LIFETEST statement in SAS 9.1 or later, then the OUTSURV= dataset is disabled (it will contain no observations). For details, see this SAS Note.

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