# st: stir and comparison of mortality rate between 2 groups

 From Hello Hello To statalist@hsphsun2.harvard.edu Subject st: stir and comparison of mortality rate between 2 groups Date Thu, 28 May 2009 19:28:30 -0700 (PDT)

```Please bear me if the question is too simple. don’t have much experience doing survival analysis and can not find the answer in the achive

Can I use stir command to compare the mortality rate of 2 groups of patients? Patients had different followup time.
stir gave me the p-value for testing the incidence rate difference and incidence rate rate ratio. It seems if the incidence rate difference not equal zero, then the different. in my results, the p-value<0.05 (stir) but the CI of the 2 mortality rates (stptime) are overlapping with each other...

If not, what is the appropriate command to use?

as I know, one test is:
sts test var, logrank
Is it the right way to test?

.. stptime, per(1000) by(x)
x   |  person-time   failures        rate   [95% Conf. Interval]
-----------+-----------------------------------------------------------
0 |       5003.8          7   1.3989368   .6669206    2.934418
1 |       1361.4          7   5.1417658   2.451254     10..7854
-----------+-----------------------------------------------------------
total |       6365.2         14   2.1994596   1.302635     3.71372

.. stir x

note:  Exposed <-> x==1 and Unexposed <-> x==0

|   Exposed   Unexposed  |      Total
-----------------+------------------------+------------
Failure |         7           7  |         14
Time |    1361.4      5003.8  |     6365.2
-----------------+------------------------+------------
|                        |
Incidence Rate |  .0051418    .0013989  |   .0021995
|                        |
|      Point estimate    |    [95% Conf. Interval]
|------------------------+------------------------
Inc. rate diff. |         .0037428       |   -.0002046    .0076903
Inc. rate ratio |         3.675481       |    1.100107    12.27986 (exact)
Attr. frac. ex. |         .7279268       |    .0909976    .9185658 (exact)
Attr. frac. pop |         .3639634       |
+-------------------------------------------------
(midp)   Pr(k>=7) =                     0.0103 (exact)
(midp) 2*Pr(k>=7) =                     0.0205 (exact)

.. sts test x, logrank
Log-rank test for equality of survivor functions
|   Events         Events
x     |  observed       expected
------+-------------------------
0     |         7          10.63
1     |         7           3.37
------+-------------------------
Total |        14          14.00
chi2(1) =       5.15
Pr>chi2 =     0.0232

.. stcox x
Cox regression -- no ties
No. of subjects =          409                     Number of obs   =       409
No. of failures =           14
Time at risk    =  6365.199998
LR chi2(1)      =      4.39
Log likelihood  =   -79.204237                     Prob > chi2     =    0.0362
------------------------------------------------------------------------------
_t | Haz. Ratio   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
x |   3.155904   1.687085     2.15   0.032     1.106848    8.998284
------------------------------------------------------------------------------

Thanks.

Sara

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