Dear Statalist,

I am using multivariable Cox regression. My main exposure (TS_WHO_gold) is a categorical variable with three levels (normal, osteopenia, osteoporosis). Several of the covariates in the model have missing data, which are deleted by listwise deletion. My question is: How can I find the count of each exposure category after running the Cox regression? I tried merely -tab- as shown below (2,686), but it doesn't match the number of observations (2,346) in the output from -stcox- (see below).

Code:
. tab TS_WHO_gold if BMIcat_gold!=. & SmoStatPackYrs_gold_missing!=. & SES_gold!=. & COP
> Dcat_gold!=. & physact_gold!=. & alcohol_gold!=. & PartAg_gold!=. & CVD_gold!=. & canc
> er_gold!=. & chrondisADL_gold!=. & diabetes_gold!=. & musc_skel_gold!=.

     WHO BMD |
  categories |
for the HUNT |
 COPD cohort |
       using |
 forearm and |
   total hip |
    DXA meas |      Freq.     Percent        Cum.
-------------+-----------------------------------
      normal |      1,737       64.67       64.67
  osteopenia |        565       21.03       85.70
osteoporosis |        384       14.30      100.00
-------------+-----------------------------------
       Total |      2,686      100.00

Code:
. stcox i.TS_WHO_gold i.Sex ib2.BMIcat_gold i.SmoStatPackYrs_gold_missing i.SES_gold i.C
> OPDcat_gold i.physact_gold i.alcohol_gold c.PartAg_gold i.CVD_gold i.cancer_gold i.chr
> ondisADL_gold i.diabetes_gold i.musc_skel_gold if (goldcopd_HUNT==1 | goldcopd_HUNT==2
> ) & (TS_HUNT!=.) & (PartAg_gold>=40.0 & PartAg_gold<=85.0)

         failure _d:  RegisStat == 5
   analysis time _t:  (enddate-origin)/365.25
             origin:  time PartDat_gold
                 id:  PID_107945

Iteration 0:   log likelihood = -8426.7323
Iteration 1:   log likelihood = -7838.0546
Iteration 2:   log likelihood =  -7797.353
Iteration 3:   log likelihood = -7797.1758
Iteration 4:   log likelihood = -7797.1757
Refining estimates:
Iteration 0:   log likelihood = -7797.1757

Cox regression -- Breslow method for ties

No. of subjects =        2,346                  Number of obs    =       2,346
No. of failures =        1,187
Time at risk    =  27880.69268
                                                LR chi2(29)      =     1259.11
Log likelihood  =   -7797.1757                  Prob > chi2      =      0.0000

Best regards,
Sigrid