Documentation Example 2 for PROC LIFETEST

The script uses the 'Sashelp.BMT' (Bone Marrow Transplant) dataset to perform survival analyses. It demonstrates how to display the table of subjects at risk below the survival plot, perform Log-rank tests with Sidak adjustment for multiple comparisons, and compare groups to a specific control group. It also shows how to use PROC FORMAT and a DATA step to reclassify strata in a specific (non-alphabetic) order for graphs, and how to add Hall-Wellner confidence bands.

Data Analysis

Type : SASHELP

The script uses the standard 'Sashelp.BMT' table. A temporary derived table 'Bmt2' is created to illustrate the manipulation of strata order via formats.

1 Code Block

PROC PRINT

Explanation :
Displays the first 10 observations of the Sashelp.BMT table for a data overview.

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1	PROC PRINT DATA=Sashelp.BMT(obs=10);
2	RUN;

2 Code Block

PROC LIFETEST

Explanation :
Activates ODS Graphics. Performs a Kaplan-Meier survival analysis. The 'plots=survival(atrisk=...)' option displays the number of subjects at risk at specific intervals (every 500 days) below the graph. The 'adjust=sidak' option applies a Sidak adjustment to the Log-rank test p-values for multiple comparisons between groups.

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1	ods graphics on;
2
3	PROC LIFETEST DATA=sashelp.BMT plots=survival(atrisk=0 to 2500 BY 500);
4	time T * STATUS(0);
5	strata Group / test=logrank adjust=sidak;
6	RUN;

3 Code Block

PROC LIFETEST

Explanation :
Performs a comparative analysis without producing graphs ('plots=none'). The 'diff=control' option compares all other groups to the specified control group ('AML-Low Risk') with Sidak adjustment.

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1	PROC LIFETEST DATA=sashelp.BMT notable plots=none;
2	time T * STATUS(0);
3	strata Group / test=logrank adjust=sidak diff=control('AML-Low Risk');
4	RUN;

4 Code Block

PROC FORMAT

Explanation :
Creates an informat '$bmtifmt' to convert group character strings to numbers, and a format 'bmtfmt' to display these numbers as labels. This allows defining a custom sorting order.

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1	PROC FORMAT;
2	invalue $bmtifmt 'ALL' = 1 'AML-Low Risk' = 2 'AML-High Risk' = 3;
3	value bmtfmt 1 = 'ALL' 2 = 'AML-Low Risk' 3 = 'AML-High Risk';
4	RUN;

5 Code Block

DATA STEP Data

Explanation :
Creates a new table 'Bmt2' based on 'Sashelp.BMT'. The 'Group' variable is recreated numerically using the previously defined informat, forcing the internal order: 1=ALL, 2=Low Risk, 3=High Risk.

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1	DATA Bmt2;
2	SET sashelp.BMT(rename=(Group=G));
3	Group = INPUT(INPUT(G, $bmtifmt.), 1.);
4	label Group = 'Disease Group';
5	FORMAT Group bmtfmt.;
6	RUN;

6 Code Block

PROC LIFETEST

Explanation :
Performs the analysis on the sorted table 'Bmt2'. The 'order=internal' option uses the underlying numeric values (1, 2, 3) for the order of legends and curves, rather than alphabetical order. The 'atrisk(outside maxlen=13)' option places the table of subjects at risk outside the plot area and limits label length.

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1	PROC LIFETEST DATA=Bmt2 plots=s(atrisk(outside maxlen=13)=0 to 2500 BY 500);
2	time T*STATUS(0);
3	strata Group / order=internal;
4	RUN;

7 Code Block

PROC LIFETEST

Explanation :
Generates survival curves in separate panels ('strata=panel'). Adds pointwise confidence limits ('cl') and Hall-Wellner confidence bands ('cb=hw'). Deactivates ODS Graphics at the end.

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1	PROC LIFETEST DATA=Bmt2 plots=survival(cl cb=hw strata=panel);
2	time T * STATUS(0);
3	strata Group/order=internal;
4	RUN;
5
6	ods graphics off;

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