st: sts graph: different results with -atrisk- vs -risktable- option

["Alex Gamma" <alex.gamma@uzh.ch>]

Dear Statasticians,

I have multiple-record survival-time data and -stset- them as shown further
below. There are 30 records for each of 591 subjects.

My question: why do I get different numbers at risk with -sts
graph-'s -risktable- vs -atrisk- options?

With -sts graph, risktable name(risktable, replace)-, I get numbers at risk
192, 169, 102, 0 for analysis time 0, 10, 20, 30 years, respectively.

With -sts graph, atrisk name(atrisk, replace)-, I get numbers at risk
960, 382, 361, 338, 166, 328, 524, 232, 536 for the beginnings of each
interval.

I'm aware that the time points for which the numbers at risk are calculated
are not the same for the two options,
but what worries me is that -atrisk- produces numbers that are much higher
than the number of subjects in the analysis. In fact, for the first time
point, the number reported by -atrisk- (960) is exactly the 5-fold of that
reported by risktable- (192). The latter number is the right one, since it
corresponds to the total number of subjects in the analysis, as shown in the
results of -stset-.

I've searched the statalist archives, the Stata FAQ, the Stata manual entry
for sts graph, and googled "Stata risktable atrisk", but I found nothing
that addressed this discrepancy.

Further below, I'm also including the results of -sts list-. Maybe
they help diagnose the problem.

Best regards,
Alex


. stset year, id(intnr) failure(de43fail==0) origin(de4==3)
enter(year==1979) if(!missing(de43nosx3yv))

               id:  intnr
    failure event:  de43fail == 0
obs. time interval:  (year[_n-1], year]
enter on or after:  year==1979
exit on or before:  failure
   t for analysis:  (time-origin)
           origin:  de4==3
               if:  !missing(de43nosx3yv)

------------------------------------------------------------------------------
   17730  total obs.
   11814  ignored per request (if(), etc.)
    1744  obs. end on or before origin()
     165  obs. begin on or after (first) failure
------------------------------------------------------------------------------
    4007  obs. remaining, representing
     192  subjects
      67  failures in single failure-per-subject data
    4007  total analysis time at risk, at risk from t =         0
                            earliest observed entry t =         0
                                 last observed exit t =        29




. sts list

        failure _d:  de43fail == 0
  analysis time _t:  (year-origin)
            origin:  de4==3
 enter on or after:  year==1979
                id:  intnr

          Beg.          Net    Survivor
 Time    Total   Fail   Lost   Function
------------------------------------------
    5      192      1      0     0.9948
    7      191      1      0     0.9896
    9      190      4     17     0.9688
   11      169      3      0     0.9516
   12      166      2      0     0.9401
   14      164      1      0     0.9344
   15      163     10     22     0.8770
   18      131      1      0     0.8703
   20      130      9     20     0.8101
   22      101     12     18     0.7138
   27       71     14     17     0.5731
   29       40      9     31     0.4441
------------------------------------------



--
Alex Gamma Ph.D.
University Hospital of Psychiatry
Research Department
Lenggstr. 31
8032 Zurich
Switzerland

Tel: +4144 384 2621
Fax: +4144 384 2446
e-mail: alex.gamma@uzh.ch

--
Alex Gamma Ph.D.
University Hospital of Psychiatry
Research Department
Lenggstr. 31
8032 Zurich
Switzerland

Tel: +4144 384 2621
Fax: +4144 384 2446
e-mail: alex.gamma@uzh.ch 

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/