Survival Analysis, Age as Time Variable

[Leon Edelman]

    clear
    input int STUDENT int EVENT int ENTER int EXIT
    1    0    11    25
    2    0    12    25
    3    1    12    24
    4    1    12    25
    5    1    12    27
    6    0    12    26
    7    0    12    24
    8    1    12    17
    9    0    14    24
    10    1    11    24
    end

    stset EXIT, failure(EVENT == 1) enter(ENTER)

When I do that I get "at risk from t = 0"at risk from t" should be equals to "earliest observed entry"
When I add

stset EXIT, failure(EVENT == 1) enter(ENTER) origin(ENTER)

then "at risk from t = 0" and "earliest observed entry =0" does that mean time on study is now the time scale?

[Carlo Lazzaro]

Leon:
the option -origin- defines when a subject becomes at risk.

. stset EXIT, failure(EVENT == 1) enter(ENTER)

Survival-time data settings

         Failure event: EVENT==1
Observed time interval: (0, EXIT]
     Enter on or after: time ENTER
     Exit on or before: failure

--------------------------------------------------------------------------
         10  total observations
          0  exclusions
--------------------------------------------------------------------------
         10  observations remaining, representing
          5  failures in single-record/single-failure data
        121  total analysis time at risk and under observation
                                                At risk from t =         0
                                     Earliest observed entry t =        11
                                          Last observed exit t =        27

. list STUDENT EVENT ENTER EXIT _st _d _t0 _t

     +------------------------------------------------------+
     | STUDENT   EVENT   ENTER   EXIT   _st   _d   _t0   _t |
     |------------------------------------------------------|
  1. |       1       0      11     25     1    0    11   25 |
  2. |       2       0      12     25     1    0    12   25 |
  3. |       3       1      12     24     1    1    12   24 |
  4. |       4       1      12     25     1    1    12   25 |
  5. |       5       1      12     27     1    1    12   27 |
     |------------------------------------------------------|
  6. |       6       0      12     26     1    0    12   26 |
  7. |       7       0      12     24     1    0    12   24 |
  8. |       8       1      12     17     1    1    12   17 |
  9. |       9       0      14     24     1    0    14   24 |
 10. |      10       1      11     24     1    1    11   24 |
     +------------------------------------------------------+

. stset EXIT, failure(EVENT == 1) enter(ENTER) origin(ENTER)

Survival-time data settings

         Failure event: EVENT==1
Observed time interval: (origin, EXIT]
     Enter on or after: time ENTER
     Exit on or before: failure
     Time for analysis: (time-origin)
                Origin: time ENTER

--------------------------------------------------------------------------
         10  total observations
          0  exclusions
--------------------------------------------------------------------------
         10  observations remaining, representing
          5  failures in single-record/single-failure data
        121  total analysis time at risk and under observation
                                                At risk from t =         0
                                     Earliest observed entry t =         0
                                          Last observed exit t =        15

. list STUDENT EVENT ENTER EXIT _st _d _origin _t0 _t

     +----------------------------------------------------------------+
     | STUDENT   EVENT   ENTER   EXIT   _st   _d   _origin   _t0   _t |
     |----------------------------------------------------------------|
  1. |       1       0      11     25     1    0        11     0   14 |
  2. |       2       0      12     25     1    0        12     0   13 |
  3. |       3       1      12     24     1    1        12     0   12 |
  4. |       4       1      12     25     1    1        12     0   13 |
  5. |       5       1      12     27     1    1        12     0   15 |
     |----------------------------------------------------------------|
  6. |       6       0      12     26     1    0        12     0   14 |
  7. |       7       0      12     24     1    0        12     0   12 |
  8. |       8       1      12     17     1    1        12     0    5 |
  9. |       9       0      14     24     1    0        14     0   10 |
 10. |      10       1      11     24     1    1        11     0   13 |
     +----------------------------------------------------------------+

See the -Two concepts of time- paragraph, -stset entry, Stata .pdf manual.