The LIFETEST Procedure

specifies the level of significance for the % confidence intervals for the survivor, hazard, and density functions. For example, the option ALPHA=0.05 requests the 95% confidence limits for the survivor function. The default value is 0.05.

specifies the significance level for the % confidence intervals for the quartiles of the survival time. For example, the option ALPHAQT=0.05 requests a 95% confidence interval for the quartiles of the survival time. The default value is 0.05.

adds a column that represents the number of subjects at risk to the survival estimate table. Also added is a column that represents the number of events at each observed time. This option has no effect for the life-table method.

specifies the maximum time for the confidence bands. The default is the largest observed event time. If the specified BANDMAX= time exceeds the largest observed event time, it is truncated to the largest observed event time.

specifies the minimum time for the confidence bands. The default is the smallest observed event time. For the equal-precision band, if the BANDMIN= value is less than the smallest observed event time, it is defaulted to the smallest observed event time.

displays the variance of the cumulative incidence function (CIF) estimator for competing-risks data. By default, PROC LIFETEST displays the standard error of the CIF estimator.

specifies the confidence bands to be output to the OUTSURV= data set. Confidence bands are available for METHOD=KM, METHOD=BRESLOW, or METHOD=FH. You can use the following keywords:

specifies the transformation applied to to obtain the pointwise confidence intervals and the confidence bands for the survivor function in addition to the confidence intervals for the quartiles of the survival times. The following keywords can be used; the default is CONFTYPE=LOGLOG.

names the SAS data set used by PROC LIFETEST. By default, the most recently created SAS data set is used.

specifies the method of calculating the variance of the CIF estimator. When ERROR=AALEN, the variance estimator is based on the theory of counting process (Aalen 1978). When ERROR=DELTA, the delta method is used to compute the variance. By default, ERROR=AALEN. For more information, see the section Estimation of the CIF.

specifies a list of interval endpoints for the life-table method. These endpoints must all be nonnegative numbers. The initial interval is assumed to start at zero whether or not zero is specified in the list. Each interval contains its lower endpoint but does not contain its upper endpoint. When this option is used with METHOD=KM, METHOD=BRESLOW, or METHOD=FH, it reduces the number of survival estimates displayed by showing only the estimates for the smallest time within each specified interval. The INTERVALS= option can be specified in any of the following ways:

a list separated by blanks		INTERVALS=1 3 5 7
a list separated by commas		INTERVALS=1,3,5,7
x to y		INTERVALS=1 to 7
x to y BY z		INTERVALS=1 to 7 by 1
a combination of the above		INTERVALS=1,3 to 5,7

For example, the specification

intervals=5,10 to 30 by 10

produces the set of intervals

specifies the maximum value of the time variable allowed on the plots so that outlying points do not determine the scale of the time axis of the plots. This option affects only the displayed plots and has no effect on any calculations.

specifies the method to be used to compute the survival function estimates. Valid values for type are as follows:

By default, METHOD=KM.

treats missing values as valid values for the stratum variables. By default, PROC LIFETEST does not use observations that have a missing value in any stratum variables. For more information, see the section Missing Values.

produces the Nelson-Aalen estimates of the cumulative hazards and the corresponding standard errors. This option is ignored if METHOD=LT is specified.

specifies the number of intervals used to compute the life-table estimates of the survivor function. This parameter is overridden by the WIDTH= option or the INTERVALS= option. When you specify the NINTERVAL= option, PROC LIFETEST tries to find an interval that results in round numbers for the endpoints. Consequently, the number of intervals can be different from the number requested. Use the INTERVALS= option to control the interval endpoints. The default is NINTERVAL=10.

suppresses the Number Left and Number Event columns in the survival estimate table. This option has no effect for the life-table estimate.

suppresses the display of output. This option is useful when only an output data set is needed. It temporarily disables the Output Delivery System (ODS); For more information about ODS, see Chapter 23, Using the Output Delivery System.

suppresses the display of survival function estimates. Only the number of censored and event times, plots, and test results is displayed.

creates an output SAS data set to contain the point and interval estimates for the cumulative incidence function (CIF). The data set also contains the number of subjects at risk, the number of events of interest, and the number of events of all types. For more information about the contents of the OUTCIF= data set, see the section OUTCIF= Data Set.

creates an output SAS data set to contain the estimates of the survival function and corresponding confidence limits for all strata. For more information about the contents of the OUTSURV= data set, see the section OUTSURV= Data Set.

creates an output SAS data set to contain the overall chi-square test statistic for association with failure time for the variables in the TEST statement, the values of the univariate rank test statistics for each variable in the TEST statement, and the estimated covariance matrix of the univariate rank test statistics. For more information about the contents of the OUTTEST= data set, see the section OUTTEST= Data Set.

performs the analysis of the restricted mean survival time (RMST). You can specify the following options:

performs the analysis of the restricted mean time lost (RMTL). You can specify the following options:

controls the plots produced using ODS Graphics. When you specify only one plot-request, you can omit the parentheses around the plot-request. Here are some examples:

plots=none
plots=(survival(atrisk=100 to 350 by 50) logsurv)
plots(only)=hazard

ODS Graphics must be enabled before plots can be requested. For example:

ods graphics on;

proc lifetest plots=survival(atrisk);
   time T*Status(0);
run;

ods graphics off;

For more information about enabling and disabling ODS Graphics, see the section Enabling and Disabling ODS Graphics in Chapter 24, Statistical Graphics Using ODS.

If ODS Graphics is enabled but you do not specify the PLOTS= option, PROC LIFETEST produces a plot of the survivor function estimates, unless you use the FAILCODE option in the TIME statement to stipulate a competing-risks analysis. In such a case, PROC LIFETEST creates a plot of the cumulative incidence function (CIF) estimates.

You can specify the following global-plot-option:

The plot-requests and plot-request options include the following.

specifies that the OUTSURV= data set contain only those observations that are included in the INTERVALS= or TIMELIST= option. This option has no effect if the OUTSURV= option is not specified. It also has no effect if neither the INTERVALS= option nor the TIMELIST= option is specified.

specifies the tolerance for testing singularity of the covariance matrix for the rank test statistics. The test requires that a pivot for sweeping a covariance matrix be at least this number times a norm of the matrix. The default value is 1E–12.

specifies that the standard error of the survivor function (SDF_STDERR) be output to the OUTSURV= data set. If the life-table method is used, the standard error of the density function (PDF_STDERR) and the standard error of the hazard function (HAZ_STDERR) are also output.

specifies the time limit used in the estimation of the mean survival time and its standard error. The mean survival time can be shown to be the area under the Kaplan-Meier survival curve. However, if the largest observed time in the data is censored, the area under the survival curve is not a closed area. In such a situation, you can choose a time limit L and estimate the mean survival curve limited to a time L (Lee 1992, pp. 72–76). This option is ignored if the largest observed time is an event time. Valid time-limit values are as follows:

specifies a list of time points at which the Kaplan-Meier estimates are displayed. The time points are listed in the column labeled Timelist. Since the Kaplan-Meier survival curve is a decreasing step function, each given time point falls in an interval that has a constant survival estimate. The event time that corresponds to the beginning of the time interval is displayed along with its survival estimate.

sets the width of the intervals used in the life-table calculation of the survival function. This parameter is overridden by the INTERVALS= option.