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.

specifies an input data set that contains appropriate variables for annotation of the traditional graphics. The ANNOTATE= option enables you to add features (for example, labels that explain extreme observations) to plots produced on graphics devices. The ANNOTATE= option cannot be used if the LINEPRINTER option is specified or if ODS Graphics is enabled. The data set specified must be an ANNOTATE= type data set, as described in SAS/GRAPH Software: Reference.

The data set specified with the ANNOTATE= option in the PROC LIFETEST statement is "global" in the sense that the information in this data set is displayed in every plot produced by a single invocation of PROC LIFETEST.

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.

specifies the symbol value for the censored observations in traditional graphics. The value, name or ’string’, is the symbol value specification allowed in SAS/GRAPH software. The default is CS=CIRCLE. If you want to omit plotting the censored observations, specify CS=NONE. The CENSOREDSYMBOL= option cannot be used if the LINEPRINTER option is specified or if ODS Graphics is enabled.

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:

ALL

outputs both the Hall-Wellner and the equal-precision confidence bands.

EP

outputs the equal-precision confidence bands.

HW

outputs the Hall-Wellner confidence bands.

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.

ASINSQRT

the arcsine-square root transformation,

LOGLOG

the log-log transformation,

This is also referred to as the log cumulative hazard transformation since it applies the logarithmic function to the cumulative hazard function. Collett (1994) and Lachin (2000) refer to it as the complementary log-log transformation.

LINEAR

the identity transformation,

LOG

the logarithmic transformation,

LOGIT

the logit transformation,

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

specifies a descriptive string of up to 256 characters that appears in the "Description" field of the traditional graphics catalog. The description does not appear in the plots. By default, PROC LIFETEST assigns a description of the form PLOT OF vname versus hname, where vname and hname are the names of the y variable and the x variable, respectively. The DESCRIPTION= option cannot be used if the LINEPRINTER option is specified or if ODS Graphics is enabled.

specifies the symbol value for the event observations in traditional graphics. The value, name or ’string’, is the symbol value specification allowed in SAS/GRAPH software. The default is ES=NONE. The EVENTSYMBOL= option cannot be used if the LINEPRINTER option is specified or if ODS Graphics is enabled.

defines the characters used for constructing the vertical and horizontal axes of the line printer plots. The string should be four characters. The first and second characters define the vertical and horizontal bars, respectively, which are also used in drawing the steps of the Kaplan-Meier, Breslow, or Fleming-Harrington survival curve. The third character defines the tick mark for the axes, and the fourth character defines the lower left corner of the plot. The default is FORMCHAR(1,2,7,9)='|-+-'. Any character or hexadecimal string can be used to customize the plot appearance. If you use hexadecimals, you must put an x after the closing quote. For example, to send the plot output to a printer with the IBM graphics character set (1 or 2), specify the following:

formchar(1,2,7,9)='B3C4C5C0'x

Refer to the chapter titled "The PLOT Procedure" in the Base SAS Procedures Guide for further information.

specifies the graphics catalog for saving traditional graphics output from PROC LIFETEST. The default is Work.Gseg. The GOUT= option cannot be used if the LINEPRINTER option is specified or if ODS Graphics is enabled. For more information, refer to the chapter titled "The GREPLAY Procedure" in SAS/GRAPH Software: Reference.

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:

For example, the specification

intervals=5,10 to 30 by 10

produces the set of intervals

specifies an input data set that contains variables for local annotation of traditional graphics. You can use the LANNOTATE= option to specify a different annotation for each BY group, in which case the BY variables must be included in the LANNOTATE= data set. The LANNOTATE= option cannot be used if the LINEPRINTER option is specified or if ODS Graphics is enabled. The data set specified must be an ANNOTATE= type data set, as described in SAS/GRAPH Software: Reference.

If there is no BY-group processing, the ANNOTATE= and LANNOTATE= options have the same effects.

specifies that plots are produced by a line printer instead of by a graphical device.

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:

allows missing values for numeric variables and blank values for character variables as valid stratum levels. See the section Missing Values for details.

By default, PROC LIFETEST does not use observations with missing values for any stratum variables.

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.

requests that the plot of censored observations be suppressed when the LINEPRINTER and PLOTS= options are specified. This option is not needed when the life-table method is used to compute the survival estimates, because the plot of censored observations is not produced.

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); see Chapter 20, Using the Output Delivery System for more information.

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 estimates of the survival function and corresponding confidence limits for all strata. See the section OUTSURV= Data Set for more information about the contents of the 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. See the section OUTTEST= Data Set for more information about the contents of the OUTTEST= data set.

controls the line printer plots produced. You must also specify the LINEPRINTER option to obtain line printer plots. When you specify only one plot-request, you can omit the parentheses around the plot-request. Here are some examples:

 plots=s
 plots=(s ls lls)

The plot-requests include the following:

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 requesting plots. 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 21, Statistical Graphics Using ODS.

If ODS Graphics is enabled but you do not specify the PLOTS= option, then PROC LIFETEST produces a plot of the estimated survivor functions by default.

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

controls plots produced in traditional graphics. To obtain traditional graphics, you must neither enable ODS Graphics nor specify the LINEPRINTER option. For each plot-request, you can use the NAME= option to specify a name to identify the plot. The name can be specified as a SAS name or as a quoted string of up to 256 characters. Only the first eight characters are used as the entry name in the GOUT= catalog. The plot-requests include the following:

When you specify only one plot-request, you can omit the parentheses around the plot-request. Here are some examples:

 plots=s
 plots=(s(name=Surv2), h(name=Haz2))

The latter requests a plot of the estimated survivor function versus time and a plot of the estimated hazard function versus time, with Surv2 and Haz2 as their names in the GOUT= catalog, respectively.

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 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.