The LLS "Log[-Log(Survival)]" plot may not appear when using ODS
GRAPHICS requested via the SURVIVAL statement PLOTS= option, if the
following conditions occur simultaneously:

1. METHOD=LT|ACT is specified on the PROC LIFETEST statement
2. LLS is among the plots requested on the PLOTS= option of the SURVIVAL
   statement (the SURVIVAL statement produces 'ODS GRAPHICS')
3. there is no stratification (the data have only one strata)

The following ERROR may appear in the SAS log file:

   ERROR: Invalid Physical Name

The following workarounds are available:

a) Use the PLOTS=(LLS) option on the PROC LIFETEST statement instead of
the SURVIVAL statement.  This method does not produce 'ODS GRAPHICS',
and SAS/GRAPH is required.

b) Use the OUTSURV= option on the PROC LIFETEST statement to output the
survival estimates to a dataset and compute LLS=log(-log(survival))
manually in a subsequent DATA step.  Then plot LLS versus time with PROC
GPLOT.  Again, SAS/GRAPH is required.

c) In order to produce an 'ODS GRAPHICS' LLS plot:
Append a bogus stratum with one censored observation at t=0 to the
original data and in so doing create a strata variable that has two
distinct values (one for the original data and one for the bogus
singleton strata).  Use a STRATA statement in the PROC LIFETEST step
that requests PLOTS=(LLS) on the SURVIVAL statement.  Ignore or disable
the bogus strata homogeneity test results.

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